Enhanced PRACH scheme for power savings, range improvement and improved detection

ABSTRACT

Enhanced random access procedures for link-budget-limited user equipment (UE) devices are disclosed. A user equipment device may transmit a first message containing a Physical Random Access Channel (PRACH). The PRACH contains instances of a Zadoff-Chu sequence, and may be transmitted repeatedly as part of a single random attempt, to facilitate correlation data combining at the base station. The available Zadoff-Chu sequences may be partitioned among a plurality of sets, each set being associated with a respective Doppler shift range (or frequency hop pattern or time repetition pattern). A UE device may signal Doppler shift (or other information) to the base station by selection of one of the sets. The first PRACH transmission and the following PRACH transmission may occur in consecutive subframes. A UE device may select from a special set of Zadoff-Chu sequences (different from a conventional set of sequences), to signal its status as a link-budget-limited device.

PRIORITY CLAIM INFORMATION

This application claims the benefit of priority to each of the followingU.S. Provisional applications:

-   -   U.S. Provisional Application No. 62/012,234 titled “Enhanced        PRACH Scheme for Power Saving and Range Improvement”, by Tarik        Tabet, Youngjae Kim and Syed Aon Mujtaba, filed Jun. 13, 2014;    -   U.S. Provisional Application No. 62/020,842 titled “Enhanced        PRACH Scheme for Power Savings, Range Improvement and Improved        Detection”, by Tarik Tabet, Youngjae Kim and Syed Aon Mujtaba,        filed Jul. 3, 2014;    -   U.S. Provisional Application No. 62/131,167 titled “Enhanced        PRACH Scheme for Power Savings, Range Improvement and Improved        Detection”, by Tarik Tabet, Youngjae Kim and Syed Aon Mujtaba,        filed Mar. 10, 2015;    -   U.S. Provisional Application No. 62/133,232 titled “Enhanced        PRACH Scheme for Power Savings, Range Improvement and Improved        Detection”, by Tarik Tabet, Youngjae Kim and Syed Aon Mujtaba,        filed Mar. 13, 2015; and    -   U.S. Provisional Application No. 62/135,138 titled “Enhanced        PRACH Scheme for Power Savings, Range Improvement and Improved        Detection”, by Tarik Tabet, Youngjae Kim and Syed Aon Mujtaba,        filed Mar. 18, 2015.

All of the above identified applications are hereby incorporated byreference in their entireties as though fully and completely set forthherein.

FIELD

The present application relates to wireless communication devices, andmore particularly to mechanisms for enhancing random access procedurefor user equipment devices that are link budget limited (e.g., rangeconstrained).

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. In recentyears, wireless devices such as smart phones and tablet computers havebecome increasingly sophisticated. In addition to supporting telephonecalls, many mobile devices now provide access to the Internet, email,text messaging, and navigation using the global positioning system(GPS), and are capable of operating sophisticated applications thatutilize these functionalities.

In LTE, the random access procedure (referred to herein as “RACH”) is animportant procedure for synchronizing the UE device with the network(NW). RACH could be used for: initial access by the UE device; handoverof the UE device from one cell to another; RRC re-establishment; UL/DLdata arrival; positioning in RRC connected. RACH is a very importantprocedure to allow the UE to access the NW, to synchronize, and toobtain orthogonal resources. Thus, it is important to ensure that itsdetection by the NW is successful. Different methods are used currentlyin the 3GPP Specifications as follows: (a) use of differentpreambles—orthogonal or with good cross-correlation properties; (b)multiple RACH attempts (depending on the NW configuration); (c) powerramp up on each successive RACH attempt.

If the device is link budget limited, a mechanism to alleviate theeffect of bad reception of the PRACH (Physical Random Access Channel) isneeded. A device may be link budget limited, e.g., if the device isequipped with a poorly performing antenna system and/or if the device islocated in area of poor coverage (e.g., far from a base station or inthe basement of a building).

SUMMARY

Enhanced random access procedures for link-budget-limited user equipment(UE) devices are disclosed.

In order to initiate a random access procedure (RACH), a user equipmentdevice that is link budget limited may transmit a first messagecontaining a Physical Random Access Channel (PRACH) preamble. In someembodiments, the PRACH preamble may have larger subcarrier spacingand/or larger temporal width than defined for conventional PRACHformats. In some embodiments, a larger number of instances of a selectedZadoff-Chu sequence may be embedded within the PRACH preamble than inconventional PRACH formats. These features may enable the base stationto increase its probability of successful decode for UE devices that arelink budget limited.

In some embodiments, as part of a single random access attempt (RACHattempt), the UE device that is link budget limited may transmit thePRACH preamble a plurality of times, with transmission timing determinedby timing configuration information supplied by the base station. (Thetiming configuration information may determine when each of thetransmissions of the PRACH preamble is to occur.) Each retransmission ofthe PRACH preamble may be identical in structure and content to theinitial transmission. The base station may combine two or more receivedinstances of the PRACH preamble, to increase probability of successfuldecode.

The base station may transmit a second message, e.g., a random accessresponse (RAR), to the link-budget-limited UE device with repetition intime and/or with lower coding rate than conventional RAR messages. Inresponse to the second message, the link-budget-limited UE device maytransmit a third message, likewise with repetition in time and/or withlower coding rate (e.g., with lower coding rate than is conventionallyspecified for the RRC connection request message). Thus, each of themessages of the random access procedure (or any subset of thosemessages) may be enhanced, to increase the likelihood for successfulcompletion of the random access procedure when dealing with a UE devicethat is link budget limited.

In some embodiments, the PRACH preamble contains one or more instancesof a Zadoff-Chu sequence, and may be transmitted repeatedly as part of asingle RACH attempt. The base station may perform correlation datacombining over two or more received instances of the PRACH preamble,thereby increasing the probability of successful decode of the PRACHpreamble.

In some embodiments, the available Zadoff-Chu sequences (i.e., availablefor UE devices to use when attempting to perform random access) may bepartitioned among a plurality of sets, each set being associated with arespective range of Doppler shift magnitude. A link-budget-limited UEdevice may measure its Doppler shift relative to the base station, andselect one of the sets based on the measured Doppler shift magnitude. AZadoff-Chu sequence from the selected set is used for the repeatedtransmissions of the PRACH preamble. The base station may performcorrelation processing on the received instances of the PRACH preambleto identify the selected set. The identity of the selected set may beused to determine an appropriate method for combining correlation datarecords corresponding to the multiple received instances of the PRACHpreamble (or the multiple received instances of the Zadoff-Chu sequencewithin the received instances of the PRACH preamble). A complex-valuedcombining method may be better for low Doppler cases while an energycombining method may be better for high Doppler cases. The techniques ofcomplex-valued combining and energy combining are well known in thefield of signal processing.

In some embodiments, the plurality of transmissions of the PRACHpreamble may employ frequency domain hopping from one transmission tothe next. The hopping pattern may also be signaled by the set selection.(The available Zadoff-Chu sequences may be partitioned among theplurality of sets so that different sets correspond to different hoppingpatterns. For example, each set may be associated with a unique pair ofDoppler range and frequency hopping pattern.) By making the PRACHpreamble hop in the frequency domain from one transmission to the next,frequency diversity is provided, which may improve on average thelikelihood of successful decode of the PRACH preamble.

The multiple transmissions of the PRACH preamble may be performedaccording to one of a plurality of possible time repetition patterns.The time repetition pattern may be also be signaled by the setselection.

In some embodiments, a UE device that is link budget limited may beconfigured so that the first transmission of the PRACH preamble and thefollowing transmission(s) of the PRACH preamble occur consecutively intime. (Each transmission of the PRACH preamble may span one or moreconsecutive subframes in time, and follow immediately after the one ormore consecutive subframes containing the previous transmission of thePRACH preamble.) Thus, in these embodiments, the base station does notneed to signal a time repetition pattern to the link-budget-limited UEdevices.

In some embodiments, a UE device that is link budget limited maytransmit a conventional PRACH preamble over one or more consecutivesubframes, and immediately thereafter, transmit one or more repetitionsof the conventional PRACH preamble. The presence of the one or morerepetitions is a signal to the base station that the UE device is linkbudget limited. UE devices that are not link budget limited do nottransmit the one or more repetitions. Thus, for each UE deviceattempting random access, the base station is able to determine whetherthat UE device is link budget limited or not by determining whether theone or more repetitions have been transmitted.

In some embodiments, a UE device may select from a special set ofZadoff-Chu sequences (different from a conventional set of sequencesused by normal UE devices or legacy UE devices), to signal its status asa link-budget-limited device. The base station performs correlationprocessing on the one or more received instances of the PRACH preambleto determine the Zadoff-Chu sequence selected by a given UE deviceattempting random access, and determines whether the UE device is linkbudget limited or not based on whether that ZC sequence belongs to thespecial set or the conventional set.

In some embodiments, the link-budget-limited UE device may transmitPRACH information over successive available subframes in one or moreconsecutive radio frames, starting in a first available subframe of afirst of the one or more consecutive radio frames. (Available subframesare defined by the signaled PRACH configuration, i.e., the PRACHconfiguration signaled by the base station.)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem.

FIG. 2 illustrates a base station in communication with a wireless userequipment (UE) device.

FIG. 3 illustrates a block diagram of a UE, according to one embodiment.

FIG. 4 illustrates a block diagram of a base station, according to oneembodiment.

FIG. 5A illustrates a PRACH preamble being transmitted as part of anuplink frame.

FIG. 5B illustrates the structure of a conventional PRACH, according toone possible format.

FIG. 6 illustrates a cyclic prefix (CP) and sequence portion of a PRACH.

FIG. 7 illustrates one embodiment of messages exchanged between a userequipment (UE) device and base station (e.g., eNodeB) as part of arandom access procedure.

FIG. 8A illustrates an embodiment of a PRACH preamble format A,including four Zadoff-Chu sequences.

FIG. 8B illustrates one embodiment of a PRACH, including a plurality ofsegments in the frequency domain.

FIG. 9 illustrates one embodiment of a method for operating a UE deviceto facilitate a random access procedure by a link-budget-limited UEdevice.

FIG. 10 illustrates one embodiment of a method for operating a basestation to facilitate random access procedure for link-budget-limited UEdevices.

FIGS. 11 and 12 illustrate two different embodiments of a method foroperating a UE device to facilitate random access procedure by signalingDoppler category via sequence set selection.

FIGS. 13 and 14 illustrate two different embodiments of a method foroperating a base station to facilitate random access procedure based onthe signaling of Doppler category via sequence set selection.

FIG. 15 illustrates a simple example of frequency hopping over multiplePRACH transmissions, according to one embodiment.

FIG. 16 illustrates one embodiment of a method comprising thetransmission of a plurality of instances of a PRACH over consecutivesubframes of an uplink signal.

FIG. 17 illustrates one embodiment of a method comprising the receptionand accumulation of a plurality of received instances of a PRACH.

FIG. 18 illustrates one embodiment of a method for a UE device to signalits link-budget-limited status to a base station, by transmission of aconventional PRACH preamble followed immediately by one or more repeatedtransmissions of the PRACH preamble. The conventional PRACH preambletransmission and the one or more repeated PRACH preamble transmissionsare successive in time. Each transmission occupies a group of one ormore consecutive subframes. Furthermore, the groups themselves may beconsecutive in time, i.e., the first subframe of each group mayimmediately follow the last subframe of the previous group.

FIG. 19 illustrates one embodiment of a method comprising thetransmission of a conventional PRACH immediately followed by one or morerepetitions of the conventional PRACH.

FIG. 20 illustrates one embodiment of a method for determining if agiven UE device attempting random access is link budget limited or notbased on the presence or absence of one or more additional PRACHinstances (i.e., in addition to one or more initial PRACH instances thatare transmitted according to a conventional PRACH format) in an uplinksignal.

FIG. 21 illustrates one embodiment of a method for determining if agiven UE device attempting random access is link budget limited or notbased on the presence or absence of one or more additional transmissionsof a PRACH (i.e., in addition to an initial transmission of the PRACH)in an uplink signal.

FIG. 22 shows a portion of Table 5.7.2-4 (“Root Zadoff-Chu sequenceorder for preamble formats 0-3”) from 3GPP TS 36.211.

FIG. 23 shows Table 5.7.2-2 (“Ncs for preamble generation, preambleformats 0-3”) from 3GPP TS 36.211.

FIG. 24 shows a portion of Table 5.7.1-2 (“Frame structure type 1 randomaccess configuration for preamble formats 0-3”) from 3GPP TS 36.211.

FIG. 25 illustrates one embodiment of a method for a UE device to signalits link-budget-limited status to a base station, by selection from aspecial set of Zadoff-Chu sequences not used by conventional UE devices.

FIG. 26 illustrates one embodiment of a method for a base station todetermine if a given UE device attempting random access is link budgetlimited or not by determining whether the PRACH preamble transmitted bythe UE device uses a ZC sequence selected from a special set of ZCsequences or from a conventional set of ZC sequences.

While features described herein are susceptible to various modificationsand alternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to be limiting to the particular form disclosed, but onthe contrary, the intention is to cover all modifications, equivalentsand alternatives falling within the spirit and scope of the subjectmatter as defined by the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS Acronyms

Various acronyms are used throughout the present disclosure. Definitionsof the most prominently used acronyms that may appear throughout thepresent disclosure are provided below:

BS: Base Station

DL: Downlink

LTE: Long Term Evolution

MIB: Master Information Block

NW: Network

PBCH: Physical Broadcast Channel

PRACH: Physical Random Access Channel

PUSCH: Physical Uplink Shared Channel

RACH: Random Access Channel

RRC: Radio Resource Control

RRC IE: RRC Information Element

RX: Reception

SFN: System Frame Number

SIB: System Information Block

TTI: Transmit Time Interval

TX: Transmission

UE: User Equipment

UL: Uplink

UMTS: Universal Mobile Telecommunication System

ZC sequence: Zadoff-Chu sequence

3GPP: Third Generation Partnership Project

Terminology

The following is a glossary of terms that may appear in the presentapplication:

Memory Medium—Any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a CD-ROM, floppy disks 104, or tape device; a computer systemmemory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM,Rambus RAM, etc.; a non-volatile memory such as a Flash, magnetic media,e.g., a hard drive, or optical storage; registers, or other similartypes of memory elements, etc. The memory medium may comprise othertypes of memory as well or combinations thereof. In addition, the memorymedium may be located in a first computer system in which the programsare executed, or may be located in a second different computer systemwhich connects to the first computer system over a network, such as theInternet. In the latter instance, the second computer system may provideprogram instructions to the first computer system for execution. Theterm “memory medium” may include two or more memory mediums which mayreside in different locations, e.g., in different computer systems thatare connected over a network.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Computer System (or Computer)—any of various types of computing orprocessing systems, including a personal computer system (PC), mainframecomputer system, workstation, network appliance, Internet appliance,personal digital assistant (PDA), television system, grid computingsystem, or other device or combinations of devices. In general, the term“computer system” can be broadly defined to encompass any device (orcombination of devices) having at least one processor that executesinstructions from a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™, PlayStation Portable™, Gameboy Advance™,iPhone™), wearable devices (e.g., smart watch), laptops, PDAs, portableInternet devices, music players, data storage devices, or other handhelddevices, etc. In general, the term “UE” or “UE device” can be broadlydefined to encompass any electronic, computing, and/ortelecommunications device (or combination of devices) which is easilytransported by a user and capable of wireless communication.

Base Station (BS)—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Processing Element—refers to various elements or combinations ofelements. Processing elements include, for example, circuits such as anASIC (Application Specific Integrated Circuit), portions or circuits ofindividual processor cores, entire processor cores, individualprocessors, programmable hardware devices such as a field programmablegate array (FPGA), and/or larger portions of systems that includemultiple processors.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIGS. 1 and 2—Communication System

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem. It is noted that the system of FIG. 1 is merely one example of apossible system, and embodiments disclosed herein may be implemented inany of various systems, as desired.

As shown, the exemplary wireless communication system includes a basestation 102 which communicates over a transmission medium with one ormore user devices 106-A through 106-N. Each of the user devices may bereferred to herein as a “user equipment” (UE) or UE device. Thus, theuser devices 106 are referred to as UEs or UE devices.

The base station 102 may be a base transceiver station (BTS), and mayinclude hardware that enables wireless communication with the UEs 106Athrough 106N. The base station 102 may also be equipped to communicatewith a network 100 (e.g., an infrastructure network of a wirelessservices provider, a core network of a cellular service provider, atelecommunication network such as a public switched telephone network(PSTN), and/or the Internet, among various possibilities). Thus, thebase station 102 may facilitate communication between the user devicesand/or between the user devices and the network 100. The communicationarea (or coverage area) of the base station may be referred to as a“cell.”

The base station 102 and the user devices may be configured tocommunicate over the transmission medium using any of various radioaccess technologies (RATs), also referred to as wireless communicationtechnologies, or telecommunication standards, such as GSM, UMTS (WCDMA),LTE, LTE-Advanced (LTE-A), 3GPP2 CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD,eHRPD), Wi-Fi, WiMAX, etc.

UE 106 may be configured to communicate using multiple wirelesscommunication standards. For example, a UE 106 might be configured tocommunicate using a 3GPP cellular communication standard (such as LTE)and/or a 3GPP2 cellular communication standard (such as a cellularcommunication standard in the CDMA2000 family of cellular communicationstandards). Base station 102 and other similar base stations operatingaccording to the same or a different cellular communication standard maythus be provided as one or more networks of cells, which may providecontinuous or nearly continuous overlapping service to UE 106 andsimilar devices over a wide geographic area via one or more cellularcommunication standards.

The UE 106 may also or alternatively be configured to communicate usingWLAN, Bluetooth, one or more global navigational satellite systems(GNSS, e.g., GPS or GLONASS), one and/or more mobile televisionbroadcasting standards (e.g., ATSC-M/H or DVB-H), etc. Othercombinations of wireless communication standards (including more thantwo wireless communication standards) are also possible.

FIG. 2 illustrates user equipment 106 (e.g., one of the devices 106-Athrough 106-N) in communication with the base station 102. The UE 106may be a device with wireless network connectivity such as a mobilephone, a hand-held device, a computer or a tablet, a wearable device, orany type of wireless device. The UE 106 may include a processor that isconfigured to execute program instructions stored in memory. The UE 106may perform any of the method embodiments described herein by executingsuch stored instructions. Alternatively, or in addition, the UE 106 mayinclude a programmable hardware element such as an FPGA(field-programmable gate array) that is configured to perform any of themethod embodiments described herein, or any portion of any of the methodembodiments described herein. The UE 106 may be configured tocommunicate using one or more wireless communication protocols. Forexample, the UE 106 may be configured to communicate using one or moreof CDMA2000, LTE, LTE-A, WLAN, GNSS, etc.

The UE 106 may include one or more antennas for communicating using oneor more wireless communication protocols. In some embodiments, the UE106 may share one or more parts of a receive chain and/or transmit chainbetween multiple wireless communication standards. The shared radio mayinclude a single antenna, or may include multiple antennas (e.g., forMIMO operation) for performing wireless communications. Alternatively,the UE 106 may include separate transmit and/or receive chains (e.g.,including separate antennas and other radio components) for eachwireless communication protocol with which it is configured tocommunicate. As another alternative, the UE 106 may include one or moreradios which are shared between multiple wireless communicationprotocols, and one or more radios which are used exclusively by a singlewireless communication protocol. For example, the UE 106 may include ashared radio for communicating using either of LTE or CDMA2000 1×RTT,and separate radios for communicating using each of Wi-Fi and Bluetooth.Other configurations are also possible.

FIG. 3—Exemplary Block Diagram of a UE

FIG. 3 illustrates an exemplary block diagram of a UE 106. As shown, theUE 106 may include a system on chip (SOC) 300, which may includeportions for various purposes. For example, as shown, the SOC 300 mayinclude processor(s) 302 which may execute program instructions for theUE 106 and display circuitry 304 which may perform graphics processingand provide display signals to the display 340. The processor(s) 302 mayalso be coupled to memory management unit (MMU) 305, which may beconfigured to receive addresses from the processor(s) 302 and translatethose addresses to locations in memory (e.g., memory 306, read onlymemory (ROM) 350, NAND flash memory 310) and/or to other circuits ordevices, such as the display circuitry 304, radio 330, connectorinterface 320, and/or display 340. The MMU 305 may be configured toperform memory protection and page table translation or set up. In someembodiments, the MMU 305 may be included as a portion of theprocessor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106. For example, the UE 106 may include various types of memory (e.g.,including NAND flash 310), a connector interface 320 (e.g., for couplingto the computer system), the display 340, and wireless communicationcircuitry (e.g., for LTE, LTE-A, CDMA2000, Bluetooth, Wi-Fi, GPS, etc.).The UE device 106 includes at least one antenna, and may includemultiple antennas, for performing wireless communication with basestations and/or other devices. For example, the UE device 106 may useantenna system 335 to perform the wireless communication.

The processor 302 of the UE device 106 may be configured to implementpart or all of the methods described herein, e.g., by executing programinstructions stored on a memory medium (e.g., a non-transitorycomputer-readable memory medium). In other embodiments, processor 302may be configured as a programmable hardware element, such as an FPGA(Field Programmable Gate Array), or as an ASIC (Application SpecificIntegrated Circuit).

FIG. 4—Exemplary Block Diagram of a Base Station

FIG. 4 illustrates a block diagram of a base station 102. It is notedthat the base station of FIG. 4 is merely one example of a possible basestation. As shown, the base station 102 may include processor(s) 404which may execute program instructions for the base station 102. Theprocessor(s) 404 may also be coupled to memory management unit (MMU)440, which may be configured to receive addresses from the processor(s)404 and translate those addresses to locations in memory (e.g., memory460 and read only memory (ROM) 450) or to other circuits or devices.

The base station 102 may include at least one network port 470. Thenetwork port 470 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above in FIGS. 1 and 2. The network port470 (or an additional network port) may also or alternatively beconfigured to couple to a cellular network, e.g., a core network of acellular service provider. The core network may provide mobility relatedservices and/or other services to a plurality of devices, such as UEdevices 106. In some cases, the network port 470 may couple to atelephone network via the core network, and/or the core network mayprovide a telephone network (e.g., among other UE devices serviced bythe cellular service provider).

The base station 102 may include at least one antenna 434. (In someembodiments, the base station includes a plurality of antennas in eachof two or more sectors.) The at least one antenna 434 may be configuredto operate as a wireless transceiver and may be further configured tocommunicate with UE devices 106 using radio 430. The antenna 434communicates with the radio 430 via communication chain 432.Communication chain 432 may be a receive chain, a transmit chain orboth. The radio 430 may be configured to communicate via one or morewireless telecommunication standards, e.g., standards such as LTE, LTE-AWCDMA, CDMA2000, etc. The processor 404 of the base station 102 may beconfigured to implement part or all of the methods described herein,e.g., by executing program instructions stored on a memory medium (e.g.,a non-transitory computer-readable memory medium). Alternatively, theprocessor 404 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (ApplicationSpecific Integrated Circuit), or a combination thereof.

Background and Problem Statement

In LTE, the random access procedure (referred to herein as “RACH”) is aprocedure for synchronizing the UE device with the network (NW). RACHmay be used for one or more of the following: initial access by the UEdevice to the NW; handover of the UE device from one cell to another;RRC re-establishment; uplink and/or downlink data arrival; positioningin RRC connected. RACH is an important procedure to allow the UE deviceto access the NW, to synchronize with uplink signals from different UEdevices, and to obtain orthogonal resources. Thus, it is important toensure that its detection by the NW is successful. Different methods areused currently in 3GPP Specifications as follows: (a) use of differentPRACH preambles—orthogonal preambles or preambles with goodcross-correlation properties—by different UE devices; (b) multiple RACHattempts (depending on the NW configuration) by the UE device; (c) rampup of power over successive RACH attempts.

If the UE device is link budget limited, a mechanism to alleviate theeffect of bad reception of PRACH (Physical Random Access Channel) isneeded. A UE device may be link budget limited, e.g., if its antennasystem is poorly performing or if the UE device is in a location wherethe signal cannot be received (such as the basement of a building, etc.)

PRACH Specifications in 3GPP

FIG. 5A illustrates a preamble 500 in a Physical Random Access Channel(PRACH) according to the existing LTE specifications. A UE devicetransmits the PRACH preamble in an uplink frame 510 in order to initiatethe random access procedure. (The uplink frame includes a plurality ofsubframes.) The time offset and frequency offset of the PRACH preamblewithin the uplink frame may be determined by the higher layer signaling.

FIG. 5B illustrates one particular realization of the PRACH preambleaccording to existing LTE specifications. In frequency, the PRACHpreamble (including the guard subcarriers at the beginning and end)spans 6 RBs=1.08 MHz. In time, the PRACH preamble, including the cyclicprefix (CP) and guard time (GT), spans one uplink sub frame.

Formats 0-3 for the PRACH preamble each use a Zadoff-Chu sequence oflength 839, whereas format 4 uses a Zadoff-Chu sequence of length 139.

The PRACH preamble occupies 6 resource bocks (RBs) in uplink bandwidth(UL BW).

One PRACH subcarrier occupies 1.25 kHz whereas a normal UL subcarrieroccupies 15 kHz. The symbols of the Zadoff-Chu sequence are transmittedon respective ones of the PRACH subcarriers.

With respect to the PRACH preamble, FIG. 6 illustrates a cyclic prefix(CP) of duration T_(CP) and a sequence portion of duration T_(SEQ). (Thesequence portion contains the Zadoff-Chu sequence.) Table 1 below showsthe values of T_(CP) and T_(SEQ) in different formats of the PRACHpreamble.

TABLE 1 Random Access Preamble Parameters Preamble Format T_(CP) T_(SEQ)0  3168 * T_(S) 24576 * T_(S) 1 21024 * T_(S) 24576 * T_(S) 2  6240 *T_(S) 2 * 24576 * T_(S)    3 21024 * T_(S) 2 * 24576 * T_(S)    4  448 *T_(S)  4096 * T_(S)Summary of RACH Procedure

The RACH procedure may involve a series of messages sent between the UEand the base station, as shown in FIG. 7.

In a first message (MSG1), the UE transmits the PRACH preamble to thebase station (i.e., eNodeB in the parlance of LTE). The PRACH preamblemay be configured according to one of the formats discussed above.

In response to decoding the first message, the eNodeB transmits a secondmessage (MSG2). The second message may be referred to as a random accessresponse (RAR).

In response to decoding the second message, the UE may transmit a thirdmessage (MSG3). The content of the third message may be different indifferent contexts, e.g., may depend on the purpose for which the RACHprocedure has been invoked. For example, the third message may includean RRC Request, SR, etc. (SR is an acronym for Scheduling Request.)

In response to receiving the third message, the eNodeB may transmit afourth message (MSG4), e.g., a contention resolution message.

PRACH Proposal for Range Extension

In some embodiments, we create a new set of preambles and resources (inthe time and/or frequency domain) specifically for use bylink-budget-limited UE devices (e.g., range-constrained UE devices).

To improve the robustness of the PRACH preamble transmission, thenumerology of the PRACH preamble may be changed, where the numerologyincludes one or more of the following:

the ZC (Zadoff-Chu) sequence length;

the subcarrier spacing of the PRACH preamble;

the number of subframes spanned by the PRACH preamble; and

the number of repetitions of the ZC sequence in the PRACH preamble.

In some embodiments, one or more of the new preambles may span aplurality of subframes.

Another way to improve robustness is to configure the UE to transmit aplurality of instances of the PRACH preamble as part of a single randomaccess attempt. This feature enables the eNB to gain the benefit ofcombining the time-domain repetitions of the PRACH preamble. Currentlyin 3GPP specifications, each RACH attempt includes only a singletransmission of the conventional PRACH preamble, and that RACH attemptis treated independently by the NW, i.e., independent of any other RACHattempt. If the UE does not receive MSG2, the UE will make another RACHattempt.

To enable the eNB to combine PRACH repetitions, the eNB may need to knowthe time of transmission of each instance of the PRACH preamble. Forexample, in some embodiments, the eNB may need to know: the startingtime of the first repetition (i.e., the first of a plurality ofinstances of the PRACH preamble); the period of time that spans all therepetitions (or, the number of repetitions and the interval of timebetween successive repetitions). In some embodiments,link-budget-limited UE devices use one of the presently-disclosed robustformats to send each repetition of the PRACH preamble while devices thatare not link budget limited send the PRACH preamble (without repetition)using a conventional format.

In some embodiments, a link-budget-limited UE device may transmit aplurality of repetitions of the PRACH preamble over a set of consecutivesubframes. For example, the PRACH preamble may span one subframe intime, and the link-budget-limited UE device may transmit one PRACHpreamble repetition in each of the consecutive subframes. As anotherexample, the PRACH preamble may span two subframes in time, and thelink-budget-limited UE device may transmit one PRACH preamble repetitionin each successive pair of the consecutive subframes. Thus, the eNB mayneed to know the starting time of the first repetition, and the numberof PRACH repetitions.

In some embodiments, the robustness of MSG2 and MSG3 of the randomaccess procedure may also need to be improved. Hence, an earlyindication to the NW that the UE device is link budget limited may beneeded. That indication may be provided by the RRC layer signaling.

The present patent discloses a number of new formats for the PRACHpreamble, including the formats described below.

New Format A for the PRACH Preamble

The new format A for the PRACH preamble may occupy 3 ms in time domain.

The new subcarrier spacing for format A may be 1.5 kHz. With asubcarrier spacing of 1.5 kHz, one can fit 720 subcarriers in 1.08 MHz.The ZC sequence length needs to be a prime number. Any of the followingsequence lengths may be used for format A:

-   -   Nzc=719, 1 subcarrier is left as guard band;    -   Nzc=709, 6 subcarriers on the left and 5 on the right are left        as guard band;    -   Nzc=701, 10 subcarriers on the left and 9 on the right are left        as guard band;    -   Nzc=691, 15 subcarriers on the left and 14 on the right are left        as guard band.

Tseq for format A may be 81920 Ts=4×20480 Ts, where Ts=1/30.72microseconds. This implies that 4 ZC sequences can be repeated in 3subframes. FIG. 8A illustrates an embodiment of how the 4ZC sequencesmay be embedded in the PRACH preamble.

For format A, Tcp=5120 Ts and GT=5120 Ts. (CP denotes the Cyclic Prefix.GT denotes the Guard Time.)

New Format B for the PRACH Preamble

The new format B for the PRACH preamble may occupy 3 ms in time domain.

The new subcarrier spacing for format B may be 2.5 kHz. With asubcarrier spacing of 2.5 kHz, one can fit 144 subcarriers in 360 kHz (2RBs). The ZC sequence length needs to be a prime number. Any of thefollowing sequence lengths may be used for format B:

-   -   Nzc=139, 2 subcarriers on the left and 2 on the right are left        as guard band;    -   Nzc=131, 7 subcarriers on the left and 6 on the right are left        as guard band (the guard band is 13×2.5 kHz which is comparable        to 25×1.25 kHz as per current 3GPP specifications).

For format B, Tseq may be 86016 Ts=7×12288 Ts, where Ts=1/30.72microsec. This means 7 ZC sequences can be repeated in 3 subframes.

For format B, Tcp=3168 Ts and GT=2976 Ts.

New Format C for the PRACH Preamble

The new format C for the PRACH preamble may occupy 1 ms in time domain.

The subcarrier spacing for format C may be 1.25 kHz. With a subcarrierspacing of 1.25 KHz, we can fit 288 subcarriers in 360 kHz (2 RBs). TheZC sequence length needs to be a prime number. Thus, for example, thefollowing sequence lengths could be used for format C:

-   -   Nzc=263, 13 subcarriers on the left and 12 on the right are left        as guard band.

For format C, Tseq may be 24576 Ts with Ts=1/30.72 microsec, Tcp=3168 Tsand GT=2976 Ts.

New Format D for the PRACH Preamble

The new format D for the PRACH may occupy 1 ms in the time domain.

The subcarrier spacing for format D may be 2.5 kHz. With a subcarrierspacing of 2.5 kHz, we can fit 144 subcarriers in 360 kHz (2 RBs). TheZC sequence length needs to be a prime number. Thus, for example, thefollowing sequence lengths could be used:

-   -   Nzc=139, 3 subcarriers on the left and 3 on the right are left        as guard band.    -   Nzc=131, 5 subcarriers on the left and 4 on the right are left        as guard band (the guard band is 13×2.5 kHz which is comparable        to 25×1.25 kHz as per current 3GPP specifications).

In format D, Tseq may be 24576 Ts=2×12288 Ts, with Ts=1/30.72 microsec.This means that 2 ZC sequences can be repeated in one TTI.

It can also be envisioned that in the subcarrier spacing case above(i.e., the case of 2.5 KHz subcarrier spacing), the whole PRACH preambleoccupies only a half subframe (1 slot), i.e., one ZC sequence occupying12288 Ts with Tcp=3168/2=1584 Ts and GT=2976/2=1488 Ts.

It should be understood that formats A through D illustrate only a fewof a wide variety of possible PRACH formats constructible according tothe principles herein described.

Notes Regarding Use of Formats A-D

In any of the PRACH formats, a link-budget-limited UE device maytransmit the PRACH preamble a plurality of times (in the time domain) aspart of a single random access attempt. PRACH formats C and D mayrequire more numerous retransmissions than formats A and B since formatsC and D have fewer instances of the ZC sequence per PRACH preamble.

In formats C and D, the 2 RBs occupied by the PRACH preamble can beadjacent or non-adjacent in the frequency domain (e.g., at the upper andlower edges of the uplink bandwidth, wherein the uplink bandwidth maybe, e.g., 1.4 MHz, 5 MHz or 10 MHz) to provide frequency diversity.

While the PRACH preamble is repeated in the time domain, the locationsof the 2 RBs can hop in the frequency domain from one repetition to thenext, to provide frequency diversity.

While various ones of the PRACH formats described herein are configuredto use 2 RBs for the PRACH preamble, other numbers of RBs may be used inother embodiments.

Time Repetition of the New PRACH Preamble

In order for the eNB to accumulate multiple repetitions of the PRACHpreamble (transmitted by the link-budget-limited UE device), the eNB mayneed to know the repetition pattern and the duration. In someembodiments, we propose to have multiple configurations, where eachconfiguration has a corresponding pattern of repetition.

In order to accumulate, the eNB needs to know what the duration is. Forexample, the new PRACH preamble may be sent the first time in a framewhose SFN satisfies SFN %20=0, and may be repeated once in theimmediately following frame, i.e., 1 SFN later. (M % N is shorthandnotation for “M modulo N”. SFN is an acronym for “System Frame Number”.)Currently in the 3GPP specifications, the configuration of theconventional PRACH preamble is given in the following table, which is acopy of Table 5.7.1-2 from specification 3GPP TS 36.211. (TS is anacronym for Technical Specification.)

TABLE 2 PRACH Configuration Example PRACH Config. Preamble System FrameSubframe Index Format Number (SFN) Number 0 0 Even 1 1 0 Even 4 2 0 Even7 3 0 Any 1

In some embodiments, we propose expanding this table, e.g., by addingone or more of the following items: a column to indicate the SFN of thefirst transmission of the PRACH preamble; a column for the number ofrepetitions of the PRACH preamble after the first transmission; a columnfor the time locations of the repetitions with respect to the firsttransmission; and a column to indicate the frequency hopping pattern forthe RBs of the PRACH preamble across the plurality of repetitions.

The UE device may detect the SFN from the MIB in the PBCH of thedownlink signal transmitted by the eNB. For handover, however, the UEdoes not need to read the MIB before initiating a random accessprocedure (RACH).

In some embodiments, in order to solve this problem of knowing the SFNof the target cell, we propose one or more of the following.

(1) Modify the UE implementation so that the UE proactively reads theMIB of the target cell before initiating a RACH procedure. (The “targetcell” means the cell that the UE is being handed over to.)

(2) For LTE Release 12 and beyond, all the eNBs will eventually be SFNsynchronized, so the SFN of the origin cell and target cell will besimilar. Therefore, the UE knows the SFN of the target cell, assuming ithas already entered the network.

(3) Modify the RRC IE MobilityControlInfo in the RRC specification (inTS 36.331) by adding the SFN of the target cell to this informationelement.

New Configuration Index Signaling

In some embodiments, the NW may signal two configurations, one fornormal UEs and one for link-budget-limited UEs.

RRC IE PRACH-Config may be extended to include aRangeConstrainedPrach-ConfigIndex.

The resources used for the link-budget-limited UEs may be reserved anddistinct from the resources used by the normal UEs (i.e., UEs that arenot link budget limited). The eNBs will be then able to detect suchpreambles.

In some embodiments, a link-budget-limited UE will signal to the NW itsstatus as a link-budget-limited UE by sending a PRACH preamble using anew PRACH format (e.g., one of the new formats described above). Incontrast, a UE that is not link budget limited may signal to the NW itsstatus of being “not link budget limited” by sending a PRACH preambleusing a conventional PRACH format. Thus, the eNB may determine thestatus of any given UE by determining which format the UE has used totransmit the PRACH preamble.

The eNB will then send MSG2 such that the probability of successfuldecode of MSG2 by the UE is sufficiently large, e.g., by lowering thecoding rate for the transmission of MSG2 and/or repeating in time (TTIBundling) the transmission of MSG2. Similarly, the UE may send the MSG3such that the probability of successful decode of MSG3 by eNB issufficiently large, e.g., by lowering the coding rate for thetransmission of MSG2 and/or repeating in time the transmission of MSG3.(The resources for MSG3 may be provided in MSG2 payload.)

In some embodiments, the eNB may also decide to offload thelink-budget-limited UEs (or a subset thereof) to one or more small cellsthat have better coverage than the eNB.

The following table describes PRACH-Config field descriptions.

PRACH-Config field descriptions rootSequenceIndex Parameter:RACH_ROOT_SEQUENCE, see TS 36.211 [21, 5.7.1]. prach-ConfigIndexParameter: prach-ConfigurationIndex, see TS 36.211 [21, 5.7.1].highSpeedFlag Parameter: High-speed-flag, see TS 36.211, [21,5.7.2].TRUE corresponds to Restricted set and FALSE to Unrestricted set.zeroCorrelationZoneConfig Parameter: Ncs configuration, see TS 36.211,[21, 5.7.2: table 5.7.2-2] for preamble format 0..3 and TS 36.211, [21,5.7.2: table 5.7.2-3] for preamble format 4. prach-FreqOffset Parameter:prach-FrequencyOffset, see TS 36.211, [21, 5.7.1]. For TDD the valuerange is dependent on the value of prach-ConfigIndex.PRACH Repetition in Frequency

In some embodiments, as part of a single random access attempt, alink-budget-limited UE device may repeat the new RACH format in thefrequency domain (in addition to, or as an alternative to, theabove-described repetition in the time domain). FIG. 8B illustrates aPRACH preamble transmission including two segments 810 and 815, whichoccupy disjoint portions of the UL frequency band, but occupy the sameinterval 805 in time. (While FIG. 8B illustrates a PRACH preambletransmission including two segments, more generally, any number ofsegments may be included in the PRACH preamble transmission.) Each ofthe segments may be identical in content and structure, e.g., mayinclude the same number of instances of the same ZC sequence. Thesegments could be separated in the frequency domain to provide thebenefit of frequency diversity, e.g., 3 RBs (or 1 RB) at the upper endof the system bandwidth and the other 3 RBs (or 1 RB) at the lower endof the system bandwidth. Each segment may be formatted as variouslydescribed above.

In some embodiments, an initial PRACH preamble transmission may befollowed by a temporal sequence of one or more re-transmissions of thePRACH preamble, e.g., as variously described above. Each of the PRACHpreamble transmissions (i.e., initial transmission and re-transmissions)may include a plurality of segments as described immediately above. Forexample, each PRACH preamble transmission may occupy a correspondingperiod in time but different portions of the UL frequency band.

Doppler Indication by PRACH Sequence

As explained above, the PRACH sequence can be sent across multiplesubframes that are separated in time. In order to obtain a maximum gainwhile detecting the sequence by the eNB, the eNB may need to know theDoppler shift or the range of Doppler shift. If the Doppler shift issmall in magnitude, then the eNB can combine the complex values of thecross-correlation across multiple subframes since the channel has notchanged much between subframes. However, if the Doppler shift is largein magnitude, then the eNB can compute the energy values correspondingto the complex values (i.e., z→|z|²=zz*), and combine the energy valuesacross multiple subframes instead of the complex values.

In some embodiments, we propose to divide the ZC sequences into aplurality of sets (e.g., 2 or 3 sets). For example, a first set of theZC sequences may be assigned for use when Doppler shift is low, a secondset of ZC sequences may be assigned for use when Doppler shift ismedium, and a third set of ZC sequences may be assigned for use whenDoppler shift is high.

We may assume that the UE and eNB have agreed upon the definition ofthese sequence sets.

The UE could use its sensors (e.g., motion sensors) to measure theDoppler shift.

The UE may select one of the sequence sets based on the measuredDoppler. The UE will use a ZC sequence from the selected sequence set toperform the multiple transmissions of the PRACH. By correlating againstthe space of possible ZC sequences, the eNB can identify the employed ZCsequence and the selected set. The identity of the selected set informsthe eNB of the category of Doppler magnitude (e.g., low, medium, high),and thus, which correlation combining method will be most effective forthe present series of PRACH transmissions. This mechanism for signallingDoppler category will improve the PRACH detection by the eNB.

Set Identity Mapping to Doppler Category, Time Pattern and FrequencyHopping Pattern

In some embodiments, the ZC sequence sets defined for different Dopplercategories are also associated with different repetition patterns intime and different frequency domain hopping patterns. In someembodiments, there are 3 sets, where each set is associated with: acorresponding Doppler category (e.g., low or medium or high); a temporalpattern for the PRACH transmissions, defining the set of TTIs where thePRACH transmissions occur in time domain; and a correspondingfrequency-hopping pattern, defining the set of frequency domains RBsoccupied by the hopping pattern. For example, in one embodiment, thethree sets are defined as follows:

Set S1 for Low Doppler: includes 20 sequences; first transmission ofPRACH sent on subframe 1, repeated every SFN for 4 SFNs; hopping withinthe range RB0:15. (RB is an acronym for “Resource Block”. RB0:15 isnotation for the resource block range given by block numbers {0, 1, . .. , 15}.)

Set S2 for Medium Doppler: includes 15 sequences; first transmission ofPRACH sent on subframe 3, repeated transmission every SFN for 4 SFNs;hopping within the range RB16:33.

Set S3 for High Doppler: includes 10 sequences; first transmission ofPRACH sent on subframe 2, repeated transmission every SFN for 4 SFNs;hopping within the range RB35:48.

Method 900 for Operating a User Equipment Device

In one set of embodiments, a method 900 for operating a user equipment(UE) device may be performed as illustrated in FIG. 9. (Method 900 mayalso include any subset of the features, elements and embodimentsdescribed above.) The method 900 may be performed by alink-budget-limited UE device to facilitate a random access procedure.The method may be implemented by a processing agent of thelink-budget-limited UE device. The processing agent may be realized byone or more processors executing program instructions, by one or moreprogrammable hardware elements, by one or more dedicated hardwaredevices such as ASICs, or by any combination of the foregoing.

The method may include transmitting a first message including at leastthree instances of a Zadoff-Chu sequence, as indicated at 910. (Forexample, in format A it is repeated 4 times, and in format B it isrepeated 7 times.) The first message may be transmitted on a physicalrandom access channel (PRACH) within a time-frequency resource space.The larger number of ZC instances allows for higher probability ofmessage decoding by the base station.

In some embodiments, the method 900 may also include performing one ormore retransmissions of the first message, wherein said transmission andsaid one or more retransmissions occur according to a pattern of timesdetermined by configuration information transmitted by a first basestation. (The initial transmission of the first message and the one ormore retransmissions occur as part of a single random access attempt bythe link-budget-limited UE device.) Thus, the base station can predictwhen the transmission and one or more retransmissions will occur, andcan combine two or more received versions of the first message,resulting in increased probability of successful decoding.

In some embodiments, the configuration information determines thepattern of times so that a first set of time-frequency resources usableby the UE device to perform said transmission and said one or moreretransmissions is different from a second set of time-frequencyresources usable by one or more other UE devices (e.g., UE devices thatare not link budget limited) to transmit conventional random accesspreambles. Each of the conventional random access preambles includes atmost two instances of a Zadoff-Chu sequence.

In some embodiments, the method 900 may also include: when a handover ofthe UE from the first base station to a second base station is beingperformed, receiving a master information block (MIB) from the secondbase station prior to said transmitting the first message, wherein theMIB includes a system frame number (SFN) associated with the second basestation, wherein the system frame number is used to determine when atime has arrived for performing said transmitting the first message.

In some embodiments, the method 900 may also include: when a handover ofthe UE from the first base station to a second base station is beingperformed, determining when a time has arrived for performing saidtransmission of the first message based on a system frame numberreceived from the first base station, wherein the system frame number issynchronized between the first base station and the second base station.

In some embodiments, the method 900 may also include: when a handover ofthe UE from the first base station to a second base station is beingperformed, receiving a radio resource control (RRC) information elementtransmitted by the first base station. The RRC information element mayinclude a system frame number associated with the second base station.The system frame number may be used to determine when a time has arrivedfor performing said transmission of the first message.

In some embodiments, the action of transmitting the first message andsaid one or more retransmissions are performed in response to storedinformation indicating that the UE is link budget limited (e.g., byvirtue of being equipped with a poorly performing antenna system).

In some embodiments, the action of transmitting the first message andsaid one or more retransmissions are performed in response to the UEdetermining that the UE is operating in a link-budget-limited condition.

In some embodiments, the method 900 may also include: prior to theaction of transmitting the first message, receiving the configurationinformation transmitted by the base station. The base station maytransmit the configuration information, e.g., as part of the systeminformation block SIB2.

In some embodiments, the configuration information identifies thepattern of times from a predefined set of timing patterns, wherein eachof the timing patterns. For example, each timing pattern may indicateallowed times for said transmission of the first message and acorresponding inter-transmission time spacing for the one or moreretransmissions.

In some embodiments, the first message includes a plurality ofsubcarriers for conveying said at least three instances of theZadoff-Chu sequence, wherein a spacing of the subcarriers is greaterthan 1.25 kHz.

In some embodiments, the first message spans more than one transmissiontime interval (TTI).

In some embodiments, the method 900 may also include: receiving a secondmessage (e.g., a random access response) transmitted by a base station,wherein the second message is transmitted by the base station inresponse to the base station successfully decoding the first message.

In some embodiments, the second message is transmitted by the basestation two or more times and/or with lower coding rate.

In some embodiments, the second message is transmitted by the basestation with a coding rate lower than conventional random accessresponse messages (e.g., conventional RAR messages as defined inexisting 3GPP standards).

In some embodiments, the method 900 may also include: transmitting athird message to the base station in response to successfully decodingthe second message from the base station. The third message may betransmitted (a) with lower coding data rate than conventional PUSCHmessages and/or (b) repeatedly in time.

Method for Operating a Base Station

In one set of embodiments, a method 1000 for operating a base station(BS) may be performed as illustrated in FIG. 10. (Method 1000 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 1000 may be performed to facilitate random accessprocedure for link-budget-limited UE devices. The method may beimplemented by a processing agent of the base station, e.g., aprocessing agent as variously described above.

At 1010, the method may include transmitting first configurationinformation for one or more link-budget-limited user equipment (UE)devices. Each of the link-budget-limited UE devices may be configured totransmit a random access preamble and perform one or moreretransmissions of the random access preamble. The random accesspreamble includes one or more instances of a Zadoff-Chu sequence. Thefirst configuration information indicates a pattern of times (and/orother configuration features such as frequency hopping pattern) for saidtransmission and said one or more retransmissions of the random accesspreamble. In some embodiments, the random access preamble includes atleast three instances of the Zadoff-Chu sequence.

In some embodiments, operation 1010 may be omitted. For example, thepattern of times (and/or other configuration features) may have beenpreviously agreed upon by the base station and the one or morelink-budget-limited UE devices (or a subset of those devices). Thus,transmission of the first configuration information is not needed.

At 1015, the method may include receiving said transmission of therandom access preamble from a first of the one or more UE devices toobtain a first data record, i.e., a set of samples.

At 1020, the method may include receiving said one or moreretransmissions of the random access preamble from the first UE deviceto obtain respectively one or more additional data records.

At 1025, the method may include decoding the random access preamblebased on the first data record and the one or more additional datarecords.

In some embodiments, the method 1000 may also include transmittingsecond configuration information for one or more UE devices that are notlink budget limited. Each of the UE devices that are not link budgetlimited may be configured to transmit a second random access preamblebased on timing identified by the second configuration information. (Thesecond random access preamble may conform to a conventional preambleformat.) The second random access preamble transmitted by any given oneof the non-link-budget-limited UE devices includes at most two instancesof a Zadoff-Chu sequence selected by that UE device.

In some embodiments, the first configuration information and the secondconfiguration information are determined by the base station so that afirst set of time-frequency resources usable by the first UE device toperform said transmission and said one or more retransmissions of therandom access preamble is different from a second set of time-frequencyresources usable by the one or more UE devices that are not link budgetlimited to transmit the second random access preambles.

In some embodiments, the method 1000 may also include: in response todecoding the random access preamble, transmitting a random accessresponse to the first UE device, wherein the random access response istransmitted (a) with lower coding rate than conventional random accessresponses and/or (b) using a plurality of repetitions in time.

In some embodiments, the method 1000 may also include: receiving amessage from the first UE device, wherein the first UE device transmitsthe message after receiving the random access response, wherein themessage is transmitted with coding rate lower than normal PUSCH messagesand/or with a plurality of repetitions in time.

In some embodiments, the first configuration information identifies thepattern of times from a predetermined set of time patterns (known to theUE devices).

In some embodiments, the random access preamble includes a plurality ofsub-carriers for conveying said at least three instances of theZadoff-Chu sequence, wherein a spacing of the subcarriers is greaterthan 1.25 kHz.

In some embodiments, the random access preamble spans more than onetransmission time interval/subframe (TTI).

User Equipment with Signaling of Doppler Category Via Sequence SetSelection

In one set of embodiments, a method 1100 for operating a user equipment(UE) device may be performed as illustrated in FIG. 11. (Method 1100 mayalso include any subset of the features, elements and embodimentsdescribed above.) The method 1100 may be performed to facilitate randomaccess procedure for link-budget-limited UE devices. The method may beimplemented by a processing agent. The processing agent may be realizedby one or more processors executing program instructions, by one or moreprogrammable hardware elements, by one or more dedicated hardwaredevices such as ASICs, or by any combination of the foregoing.

At 1110, the processing agent may select a set from a plurality of setsof Zadoff-Chu sequences. The selection may be based on a measurement ofDoppler shift magnitude of the UE device relative to a base station. (Inalternative embodiments, the selection may be based on some otherproperty or data value or range of data values to be signaled to thebase station.) The identity of the selected set among the plurality ofsets is usable by a base station to determine a correlation accumulationmethod. Each set may include a plurality of Zadoff-Chu sequences.

The correlation accumulation method may, e.g., be selected from acomplex-valued accumulation method and an energy accumulation method,e.g., as variously described above. The set of accumulation methods fromwhich selection occurs may include other methods as well.

At 1115, the processing agent may perform two or more transmissions of afirst message. The first message may include one or more instances of aparticular Zadoff-Chu sequence chosen from the selected set.

In some embodiments, the two or more transmissions are performed withfrequency hopping over a plurality of time intervals. Different ones ofthe above-described sets may be associated with different patterns offrequency hopping.

In some embodiments, the two or more transmissions are performedaccording to one of a plurality of possible repetition patterns in time.Different ones of the sets may be associated with different ones of therepetitions patterns in time.

In one set of embodiments, a method 1200 for operating a user equipment(UE) device may be performed as illustrated in FIG. 12. (Method 1200 mayalso include any subset of the features, elements and embodimentsdescribed above.) The method 1200 may be performed to facilitate arandom access procedure for link-budget-limited UE devices. The method1200 may be implemented by a processing agent. The processing agent maybe realized by one or more processors executing program instructions, byone or more programmable hardware elements, by one or more dedicatedhardware devices such as ASICs, or by any combination of the foregoing.

At 1210, the processing agent may select a set from a plurality of setsbased on a measurement of Doppler shift magnitude of UE relative to abase station. Each of the sets includes a plurality of Zadoff-Chusequences. Different ones of the sets have been assigned to differentranges of Doppler shift magnitude.

At 1215, the processing agent may perform two or more transmissions of afirst message, where the first message includes one or more instances ofa particular Zadoff-Chu sequence chosen from the selected set. The UEdevice thereby signals to the base station information regarding itsmeasured Doppler shift magnitude. The base station may use the identityof the selected set to determine an appropriate method for correlationdata combining over the two or more instances of the first message.

In some embodiments, the base station may be configured to: receivesymbol data in response to the two or more transmissions of the firstmessage; perform correlation processing on the symbol data to obtaininformation identifying the particular Zadoff-Chu sequence andinformation identifying the selected set among the plurality of sets;select a correlation accumulation method from a complex-valuedaccumulation method and an energy accumulation method based on theinformation identifying the selected set; and accumulate two or morecorrelation sequences according to the selected correlation accumulationmethod, wherein each of the two or more correlation sequences isgenerated by correlation of a respective portion of the symbol data withthe particular Zadoff-Chu sequence, wherein each of the portions of thesymbol data corresponds to a respective instance of the particularZadoff-Chu sequence in one of the two or more transmissions.

In some embodiments, each of the two or more transmissions occurs in adifferent time interval, wherein a first of the transmissions in a firsttime interval occupies a first set of frequency resources, wherein asecond of the transmissions in a second time interval occupies a secondset of frequency resources different from the first set of frequencyresources.

In some embodiments, the two or more transmissions respectively occupytwo or more distinct time intervals, wherein frequency resources used toperform the two or more transmissions change from one the time intervalsto the next according to a particular one of a plurality of frequencyhopping patterns, wherein each of the plurality frequency hoppingpatterns is associated with a respective one of the plurality of sets.

In some embodiments, the base station is configured to: receive symboldata in response to the two or more transmissions of the first message;perform correlation processing on subsets of the symbol data, whereineach of the subsets of the symbol data corresponds to a respective oneof the frequency hopping patterns, wherein the correlation processingdetermines information identifying the particular Zadoff-Chu sequenceand information identifying the selected set among the plurality of setsof Zadoff-Chu sequences; and accumulate two or more correlationsequences generated by correlating two or more respective portions of aparticular subset of the symbol data with the particular Zadoff-Chusequence, wherein the particular subset of the symbol data is chosenbased on the information identifying the selected set of Zadoff-Chusequences, wherein each of the two or more portions of the particularsubset corresponds to a respective instance of the particular Zadoff-Chusequence in one of the two or more transmissions of the first message.

In some embodiments, the two or more transmissions are performedaccording to one of a plurality of repetition patterns in time, whereineach of the repetition patterns in time is associated with a respectiveone of the sets of Zadoff-Chu sequences.

In some embodiments, the base station is configured to: receive symboldata in response to the two or more transmissions of the first message;perform correlation processing on subsets of the symbol data, whereineach of the subsets corresponds to a respective one of the repetitionspatterns in time, wherein the correlation processing determinesinformation identifying the particular Zadoff-Chu sequence andinformation identifying the selected set among the plurality of sets ofZadoff-Chu sequences; and accumulate two or more correlation sequencesto obtain an accumulated correlation sequence, wherein the two or morecorrelation sequences are generated by correlating two or morerespective portions of a particular subset of the symbol data with theparticular Zadoff-Chu sequence, wherein the particular subset of thesymbol data is chosen based on the information identifying the selectedset of Zadoff-Chu sequences, wherein each of the two or more respectiveportions corresponds to a respective instance of the particularZadoff-Chu sequence in one of the two or more transmissions of the firstmessage.

Base Station Selects Correlation Accumulation Method Based on SetMembership of Zadoff-Chu Sequence

In one set of embodiments, a method 1300 for operating a base stationmay be performed as illustrated in FIG. 13. (Method 1300 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 1300 may be performed to facilitate random accessprocedure for link-budget-limited UE devices. The method 1300 may beimplemented by a processing agent. The processing agent may be realizedby one or more processors executing program instructions, by one or moreprogrammable hardware elements, by one or more dedicated hardwaredevices such as ASICs, or by any combination of the foregoing.

At 1310, the processing agent may receive symbol data in response to twoor more transmissions of a first message from the UE device, e.g., asvariously described above. The UE device may perform the two or moretransmissions using a particular Zadoff-Chu sequence chosen from one ofa plurality of sets of Zadoff-Chu sequences.

At 1315, the processing agent may perform correlation processing on thesymbol data to identify the set to which the particular Zadoff-Chusequence belongs.

At 1320, the processing agent may accumulate correlation data recordsusing an accumulation method. The accumulation method may be selectedfrom a complex-valued accumulation method or an energy accumulationmethod based on the identity of said set.

In some embodiments, the UE device performs the two or moretransmissions using frequency hopping over a plurality of timeintervals, wherein different ones of the sets are associated withdifferent patterns of frequency hopping. In these embodiments, themethod may also include determining the frequency hopping pattern basedon the identity of said set.

In some embodiments, the UE device performs the two or moretransmissions according to one or a plurality of possible repetitionspatterns in time, wherein different ones of the sets are associated withdifferent repetition patterns in time. In these embodiments, the methodmay also include determining the repetition pattern based on theidentity of said set.

In some embodiments, the correlation accumulation method is selectedfrom a complex-valued accumulation method and an energy accumulationmethod.

In one set of embodiments, a method 1400 for operating a base stationmay be performed as illustrated in FIG. 14. (Method 1400 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 1400 may be performed to facilitate random accessprocedure for link-budget-limited UE devices. The method 1400 may beimplemented by a processing agent. The processing agent may be realizedby one or more processors executing program instructions, by one or moreprogrammable hardware elements, by one or more dedicated hardwaredevices such as ASICs, or by any combination of the foregoing.

At 1410, the processing agent may receive symbol data in response to twoor more transmissions of a first message from the UE device, wherein thefirst message includes one or more instances of a particular Zadoff-Chusequence, wherein the particular Zadoff-Chu sequence has been chosen bythe UE device from a selected one of a plurality of sets of Zadoff-Chusequences, wherein each of the sets corresponds to a different range ofmagnitude of Doppler shift of the UE device relative to the base station

At 1415, the processing agent may perform correlation processing on thesymbol data to determine information identifying the particularZadoff-Chu sequence and information identifying the selected set amongthe plurality of sets.

At 1420, the processing agent may select a correlation accumulationmethod from a complex-valued accumulation method and an energyaccumulation method based on the information identifying the selectedset.

At 1425, the processing agent may accumulate two or more correlationsequences according to the selected correlation accumulation method.Each of the two or more correlation sequences may be generated bycorrelation of a respective portion of the symbol data with theparticular Zadoff-Chu sequence. Each of the portions of the symbol datamay correspond to a respective instance of the particular Zadoff-Chusequence in one of the two or more transmissions.

In some embodiments, each of the two or more transmissions occurs in adifferent time interval. A first of the transmissions in a first timeinterval may occupy a first set of frequency resources; and a second ofthe transmissions in a second time interval may occupy a second set offrequency resources different from the first set of frequency resources.

In some embodiments, the two or more transmissions respectively occupytwo or more distinct time intervals, where frequency resources used toperform the two or more transmissions change from one the time intervalsto the next according to a particular one of a plurality of frequencyhopping patterns, wherein each of the plurality frequency hoppingpatterns is associated with a respective one of the plurality of sets.

In some embodiments, the method 1400 may also include: receiving symboldata in response to the two or more transmissions of the first message;performing correlation processing on subsets of the symbol data, whereineach of the subsets of the symbol data corresponds to a respective oneof the frequency hopping patterns, wherein the correlation processingdetermines information identifying the particular Zadoff-Chu sequenceand information identifying the selected set among the plurality of setsof Zadoff-Chu sequences; accumulating two or more correlation sequencesgenerated by correlating two or more respective portions of a particularsubset of the symbol data with the particular Zadoff-Chu sequence,wherein the particular subset of the symbol data is chosen based on theinformation identifying the selected set of Zadoff-Chu sequences,wherein each of the two or more portions of the particular subsetcorresponds to a respective instance of the particular Zadoff-Chusequence in one of the two or more transmissions of the first message.

In some embodiments, the two or more transmissions are performedaccording to one of a plurality of repetition patterns in time, whereineach of the repetition patterns in time is associated with a respectiveone of the sets of Zadoff-Chu sequences.

In some embodiments, the method 1400 may also include: receiving symboldata in response to the two or more transmissions of the first message;performing correlation processing on subsets of the symbol data, whereineach of the subsets corresponds to a respective one of the repetitionspatterns in time, wherein the correlation processing determinesinformation identifying the particular Zadoff-Chu sequence andinformation identifying the selected set among the plurality of sets ofZadoff-Chu sequences; and accumulating two or more correlation sequencesto obtain an accumulated correlation sequence, wherein the two or morecorrelation sequences are generated by correlating two or morerespective portions of a particular subset of the symbol data with theparticular Zadoff-Chu sequence, wherein the particular subset of thesymbol data is chosen based on the information identifying the selectedset of Zadoff-Chu sequences, wherein each of the two or more respectiveportions corresponds to a respective instance of the particularZadoff-Chu sequence in one of the two or more transmissions of the firstmessage.

In some embodiments, the first message includes two instances of theparticular Zadoff-Chu sequence.

Example of Frequency Hopping Over Multiple PRACH Transmissions

FIG. 15 illustrates a simple example of frequency hopping over multiplePRACH transmissions. Each PRACH transmission includes 2 RBs and occursin a corresponding time interval. For example, a first PRACHtransmission includes RBs 810 and 815, which occur in time interval T1;a second PRACH transmission includes RBs 820 and 825, which occur intime interval T2; a third PRACH transmission includes RBs 830 and 835,which occur in time interval T3; and a fourth PRACH transmissionincludes RBs 840 and 845, which occur in time interval T4. The pair ofRBs hops to different frequency locations in different time intervals,thus providing frequency diversity. A wide variety of otherpossibilities for the frequency hopping pattern and the varioustransmission parameters are contemplated, and the present example is notmeant to be limiting.

PRACH Repetition Over Consecutive Subframes for Link-Budget-Limited UEDevices

In some embodiments, a link-budget-limited UE device may transmit thePRACH repeatedly, over successive subframes, e.g., with one PRACHtransmission in each of the successive subframes. Thus, it may not benecessary to modify the SIB2 information. The subframe where the firstinstance of the PRACH is sent may be the subframe indicated by the SIB2as defined by existing LTE standards. (UE devices operating under theexisting LTE standards would transmit only one PRACH-containingsubframe.) UE devices that are not link budget limited (e.g., UE devicesthat are closer to the eNB) may perform random access in a conventionalmanner, using only one PRACH-containing subframe.

In any one of the successive subframes, the 2 RBs forming the PRACH forthat subframe can be adjacent or spread across the frequency domain(e.g., at the edges of 1.4 MHz, 5 MHz or 10 MHz) to benefit fromfrequency diversity. In one embodiment, new PRACH format C may be usedfor transmitting the instances of the PRACH in the correspondingsubframes. However, any of a wide variety of other formats may be used.

The number of repetitions of the PRACH may be fixed. Alternatively, thenumber of repetitions may be variable, e.g., signaled to the UE by theeNB. For example, a value may be added in SIB2, in order to signal thenumber of repetitions.

While the PRACH is repeated in the time domain, the location of the 2RBs forming the PRACH can hop in the frequency domain from one subframeto the next, allowing the eNB to benefit from frequency diversity. Thehopping pattern could either be predetermined (fixed), or signaled insystem information (e.g., SIB2) transmitted by the eNB.

In some embodiments, the RBs used by a link-budget-limited UE device forits first PRACH transmission at least partially overlap with the RBsused by a normal UE device for its only PRACH transmission. (The term“normal UE device” is a synonym for a UE device that is not link budgetlimited.) However, the link-budget-limited UE devices and normal UEdevices will use different ZC sequences, e.g., randomly chosen ZCsequences. Thus, even though link-budget-limited devices and normaldevices collide on the commonly used RBs, the ZC sequences may besufficiently orthogonal that the eNB can clearly detect the ZC sequencetransmitted by each of the devices. Link-budget-limited devices willhave additional opportunities to re-transmit PRACH in the followingconsecutive subframes.

In other embodiments, the RBs used by a link-budget-limited UE devicefor its first PRACH transmission are configured to be disjoint with theRBs used by a normal UE device for its only PRACH transmission.

FIG. 16—PRACH Instances Transmitted Over Consecutive Subframes

In one set of embodiments, a method 1600 for operating a UE device mayinclude the operations shown in FIG. 16. (The method 1600 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 1600 may be employed to facilitate a random accessprocedure when the UE device is link budget limited. The operations maybe performed by a processing agent of the UE device, e.g., a processingagent as variously described above.

At 1610, the UE device may transmit a plurality of instances of aPhysical Random Access Channel (PRACH) over a plurality of consecutivesubframes of an uplink signal to a base station. Each of the consecutivesubframes may include a corresponding one of the PRACH instances. (Theplurality of PRACH instances are preferably transmitted as part of asingle random access attempt by the UE device.) The consecutivesubframes may be subframes in a single radio frame or in a plurality ofradio frames.

In some embodiments, resource blocks used by the UE device to transmit afirst of the PRACH instances in a first of the consecutive subframes aredisjoint from resource blocks used by a second UE device to transmit aconventional PRACH subframe, where the second UE device is not linkbudget limited.

In some embodiments, resource blocks used by the link-budget-limited UEdevice to transmit a first of the PRACH instances in a first of theconsecutive subframes at least partially overlap with resource blocksused by a second UE device to transmit a conventional PRACH subframe,where the second UE device is not link budget limited. Thelink-budget-limited UE device and the second UE device may each beconfigured to randomly select a corresponding ZC root for PRACHtransmission. (Thus, the independently selected ZC roots are likely tobe sufficiently orthogonal for unique identification at the basestation.)

In some embodiments, the method 1600 may also include receiving systeminformation (e.g., as part of SIB2) that indicates the number of saidconsecutive subframes.

In some embodiments, the number of said successive subframes is fixed,and known by the link budget limited UE device and the base station.

In some embodiments, resource blocks used by the link-budget-limited UEdevice to transmit a PRACH instance hop in the frequency domain from oneof the consecutive subframes to the next.

In some embodiments, a hopping pattern according to which the resourceblocks hop in the frequency domain is fixed and known by thelink-budget-limited UE device and the base station.

In some embodiments, the method 1600 may also include receiving systeminformation (e.g., as part of SIB2) identifying a hopping pattern to beused to perform said hopping in the frequency domain.

FIG. 17—Base Station Supporting Correlation Accumulation of PRACHInstances

In one set of embodiments, a method 1700 for operating a base stationmay include the operations shown in FIG. 17. (The method 1700 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 1700 may be employed to facilitate successfulcompletion of a random access procedure when a UE device is link budgetlimited. The operations may be performed by a processing agent of thebase station, e.g., a processing agent as variously described above.

At 1710, the base station may receive symbol data in response to atransmission of a plurality of instances of a PRACH by the UE device.The plurality of PRACH instances are transmitted over a plurality ofconsecutive subframes. (The plurality of PRACH instances are transmittedas part of a single random access attempt by the UE device.) Each of theplurality of consecutive subframes contains a corresponding one of thePRACH instances.

At 1715, the base station may perform correlation processing on thesymbol data to determine which Zadoff-Chu (ZC) sequence from a set ofavailable ZC sequences is included in the plurality of PRACH instances.The correlation processing accumulates correlation data over theplurality of consecutive subframes. The accumulation of the correlationdata may have the effect of improving the probability of successfuldecode of the PRACH preamble.

Time Repetition of the New PRACH Format

In order for the eNB to accumulate the repeated PRACH transmissions overthe consecutive subframes, the eNB needs to know the number of theconsecutive subframes used by the UE to transmit the repeated PRACHtransmissions. This number could be fixed (e.g., 2 or 3 or 4 or 5), orsignaled by the eNB in system information (e.g., in a modified versionof SIB2).

The eNB may need to know the frequency hopping pattern of the RBs (e.g.,2 RBs) containing the PRACH sequence, i.e., the pattern of frequencyhopping from one subframe to the next in the set of successivesubframes. Similar to the above, the hopping pattern could either befixed (e.g., a hopping sequence for each ZC root sequence chosen by theUE) or signaled in system information such as SIB2.

Signaling Link-Budget-Limited Status by Additional PRACH Transmissions

In some embodiments, an eNB and UE devices may operate as follows toallow the eNB to determine during the initial PRACH messaging of therandom access procedure whether a given UE device is link budget limitedor not.

The eNB may transmit conventional system information (such as SIB2) tothe UE device in the cell (or sector), wherein the system informationcontrols features of the random access procedure such as PRACHconfiguration and PRACH format. For example, the eNB may signal in SIB2one of PRACH format 0 or PRACH format 2, as defined by the LTEspecifications. When initiating the random access procedure, any UEdevice, whether link budget limited or not, may transmit a conventionalset of one or two consecutive PRACH-containing subframes, using thePRACH format and the PRACH configuration signaled by the eNB, as definedby the LTE specifications. (Format 0 uses only one PRACH-containingsubframe. Format 2 uses two consecutive PRACH-containing subframes.) Alink budget limited device will continue by transmitting one or moreadditional PRACH-containing subframes that follow consecutively afterthe conventional subframe set. A UE device that is not link budgetlimited will not transmit any additional PRACH-containing subframe aspart of the present random access procedure. (Any UE device may initiatea new random access procedure if the present procedure fails.) Thenumber of the one or more additional PRACH-containing subframes used bylink budget limited devices is known by the eNB.

In other words, any UE device may transmit the one or more PRACHattempts as dictated by the existing LTE standards while the link budgetlimited UE device will transmit one or more additional PRACH subframesin each attempt, in order to signal its link budget limited status tothe eNB. The one or more additional PRACH instances occur in consecutivesubframes and start in the subframe immediately after the last subframeof the conventional subframe set.

The eNB can determine whether a UE device is link budget limited or notby analyzing the conventional subframe set, and the entire subframe set,which includes the conventional subframe set and the one or moreadditional subframes. If a UE device is link budget limited, correlationprocessing on the entire subframe set should identify a significant peak(or strong peak) for the UE-selected ZC sequence. If a UE device is notlink budget limited, correlation processing of the conventional subframeset should identify a peak for the UE-selected ZC sequence, whilecorrelation processing on the entire subframe set may fail to identify aunique peak due to the diluting (correlation destroying) effect of thenon-PRACH-bearing additional subframes.

As an example, if the eNB signals the use of format 0 and subframe 0,the link budget limited UE device may send a first PRACH instance (asdictated by format 0) in subframe 0, and an additional PRACH instance ineach of subframes 1 and 2. Each additional PRACH instance may use thesame ZC sequence, the same number or PRACH-containing resource blocks asthe first PRACH instance.

As another example, if the eNB signals the use of format 2 and subframe0, then the link budget limited UE device may send a PRACH instance ineach of subframes 0 and 1, as dictated by format 2, and then transmit anadditional PRACH instance in each of subframes 2 and 3. Each additionalPRACH instance may use the same PRACH configuration as subframes 0 and1.

In alternative embodiments, a link budget limited UE device may ignorethe PRACH format signaled by SIB2, and always use a predetermined one offormat 0 or format 2 for its initial PRACH messaging, but otherwisebehave as described above in the section “Signaling Link-Budget-LimitedStatus by Additional PRACH Transmissions”. (The predetermined format isknown to the eNB, and thus, the eNB knows to receive PRACH instancesaccording to the predetermined format.)

For example, whenever it needs to perform the random access procedure, alink budget limited UE may send format 2 in subframes 0 and 1 (format 2lasts 2 ms), and repeats in subframes 2 and 3. As another example,whenever it needs to perform the random access procedure, a link budgetlimited UE may send format 0 in subframe 0, and repeats in subframe 1and subframe 2.

FIG. 18—Method for Signaling Link Budget Limited Status to Base Station

In one set of embodiments, a method 1800 for operating a user equipment(UE) device may include the operations shown in FIG. 18. (The method1800 may also include any subset of the features, elements andembodiments described above.) The method 1800 may be employed tofacilitate successful completion of a random access procedure if (orwhen) a UE device is link budget limited. The operations may beperformed by a processing agent of the UE device, e.g., a processingagent as variously described above.

At 1810, the UE device may transmit a first set of one or more instancesof a Physical Random Access Channel (PRACH) respectively over a firstset of one or more consecutive subframes. The action of transmitting thefirst set of one or more PRACH instances may be performed according to aconventional format for transmission of PRACH.

At 1815, the UE device may transmit a second set of one or moreinstances of the PRACH respectively over a second set of one or moreconsecutive subframes starting immediately after a last subframe of thefirst set of one or more subframes. Each of the one or more PRACHinstances of the first set and each of the one or more PRACH instancesof the second set may use the same Zadoff-Chu sequence.

Operations 1810 and 1815 are performed as part of a single random accessattempt by the link-budget-limited UE device.

UE devices that are not link budget limited may be configured totransmit the one or more conventional instances of the PRACH but not theone or more additional instances. Thus, the base station is able todetermine whether a given UE device attempting random access is linkbudget limited or not by determining whether the additional instancesare present in the uplink signal.

In some embodiments, the method 1800 may also include, prior to saidtransmitting the first set of one or more PRACH instances, receivingsystem information (e.g., in SIB2) from a base station. The systeminformation may indicate at least the conventional format. (The“conventional format” may, e.g., be a format specified by 3GPP TS36.211.)

In some embodiments, the conventional format may be a fixed format knownto a base station serving the UE device.

In some embodiments, the conventional format corresponds to PRACH format0 of 3GPP TS 36.211, wherein the first set of one or more subframesincludes only one subframe.

In some embodiments, the conventional format corresponds to PRACH format2 of 3GPP TS 36.211, where the first set of one or more subframesincludes exactly two subframes.

In some embodiments, a PRACH configuration (e.g., number ofPRACH-containing resource blocks, number of ZC sequence repetitions, ZCsequence length) for each subframe of the first set and for eachsubframe of the second set is identical.

In one set of embodiments, a method 1900 for operating a user equipment(UE) device may include the operations shown in FIG. 19. (The method1900 may also include any subset of the features, elements andembodiments described above.) The method 1900 may be employed tofacilitate successful completion of a random access procedure if (orwhen) a UE device is link budget limited. The operations may beperformed by a processing agent of the UE device, e.g., a processingagent as variously described above.

At 1910, the UE device may transmit a first set of one or moreconsecutive subframes including a first Physical Random Access Channel(PRACH). The first PRACH may be transmitted according to a conventionalformat for PRACH transmission.

At 1915, the UE device may transmit a second set of one or moreconsecutive subframes containing one or more repetitions of the firstPRACH. The second set of one or more consecutive subframes may startimmediately after a last subframe of the first set of one or moresubframes. Each of the one or more PRACH repetitions may use the sameZadoff-Chu sequence as the first PRACH.

Operations 1910 and 1915 are performed as part of a single random accessattempt by the link-budget-limited UE device.

In one set of embodiments, a method 2000 for operating a base stationmay include the operations shown in FIG. 20. (The method 2000 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 2000 may be employed to facilitate successfulcompletion of a random access procedure if (or when) a UE device is linkbudget limited. The operations may be performed by a processing agent ofthe base station, e.g., a processing agent as variously described above.

At 2010, the base station may receive a first symbol data set inresponse to a first transmission by the UE device, wherein the firsttransmission includes a first set of one or more instances of a PhysicalRandom Access Channel (PRACH) respectively over a first set of one ormore consecutive subframes, wherein said first transmission is performedaccording to a conventional format for transmission of PRACH.

At 2015, the base station may receive a second symbol data set inresponse to a subsequent transmission by the UE device, wherein thesubsequent transmission includes a second set of one or more consecutivesubframes starting immediately after a last subframe of the first set ofone or more subframes.

At 2020, the base station may perform correlation processing on a unionof the first symbol data set and the second symbol data set to determineif the second set of one or more consecutive subframes contains one ormore PRACH instances in addition to the first set of one or more PRACHinstances, wherein the one or more additional PRACH instances, ifpresent, are assumed to use to the same ZC sequence as the one or morePRACH instances of the first set.

At 2025, in response to determining that the second set of one or moreconsecutive subframes contains one or more PRACH instances in additionto the first set of one or more PRACH instances, the base station maystore in memory an indication that the UE device is link budget limited.

In some embodiments, the method 2000 may also include, prior to saidreceiving the first symbol data set, transmitting system informationthat indicates at least the conventional format.

In some embodiments, the conventional format is a fixed format known tothe base station.

In some embodiments, the method 2000 may also include: in response tothe indication that the UE device is link budget limited, transmittingone or more messages of a random access procedure to the UE device usinga lower coding rate (or more redundancy) than used when non-link-budgetlimited UE devices are attempting random access.

In some embodiments, the method 2000 may also include: in response tothe indication that the UE device is link budget limited, transmittingdownlink payload data to the UE device using a lower coding rate (ormore redundancy) than used when non-link-budget limited UE devices areattempting random access.

The stored indication of link-budget-limited status of a UE device maybe used by the base station to invoke special handling procedures forthat UE device, e.g., for transmission of MSG2 and/or MSG4, and/or, forreception of MSG3 of the random access procedure, e.g., as variouslydescribed above.

In one set of embodiments, a method 2100 for operating a base stationmay include the operations shown in FIG. 21. (The method 2100 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 2100 may be employed to facilitate successfulcompletion of a random access procedure if (or when) a UE device is linkbudget limited. The operations may be performed by a processing agent ofthe base station, e.g., a processing agent as variously described above.

At 2110, the base station may receive a first symbol data set inresponse to a first transmission by the UE device, wherein the firsttransmission is a transmission of a first set of one or more consecutivesubframes including a first Physical Random Access Channel (PRACH),wherein said first PRACH is transmitted according to a conventionalformat for PRACH transmission.

At 2115, the base station may receive a second symbol data set inresponse to a subsequent transmission by the UE device, wherein thesubsequent transmission is a transmission of a second set of one or moreconsecutive subframes, wherein the second set of one or more consecutivesubframes starts immediately after a last subframe of the first set ofone or more subframes.

At 2120, the base station may perform correlation processing on a unionof the first symbol data set and the second symbol data set to determineif the second set of one or more consecutive subframes contains one ormore repetitions of the first PRACH, wherein the one or more repetitionsof the first PRACH, if present, are assumed to use to the sameZadoff-Chu sequence as the first PRACH.

At 2125, in response to determining that the second set of one or moreconsecutive subframes contains one or more repetitions of the firstPRACH, the base station may store in memory an indication that the UEdevice is link budget limited.

Background Regarding Conventional PRACH Sequence Set

In 3GPP TS 36.211, a list of logical root sequence numbers andcorresponding physical root sequence numbers is specified for PRACH. SeeFIG. 22, which shows Table 5.7.2-4 of TS 36.211. The eNB will signal alogical root sequence number in SIB2. The UE then will generate a set of64 Zadoff-Chu sequences based: on Ncs (also signaled in SIB2); andphysical root sequence numbers corresponding respectively to consecutivelogical root sequence numbers, starting with the signaled logical rootsequence number. In particular, the eNB generates a first subset of thesequences based on cyclic shifts using the first physical root sequencenumber until the first physical root sequence number is exhausted, thengenerates a second subset of sequences based on cyclic shifts using thesecond physical root sequence number until the second physical rootsequence number is exhausted, and so on, until 64 sequences have beengenerated.

FIG. 23 is a copy of Table 5.7.2-2 (“Ncs for preamble generation,preamble formats 0-3”) from 3GPP TS 36.211. The Table shows the value ofNcs for restricted set and unrestricted set, as a function ofzeroCorrelationZoneConfig.

Also the eNB will signal the PRACH configuration to the UE. The PRACHconfiguration will determine which subframes can be used by the UE tosend the PRACH preamble. See FIG. 24, which presents a table showingframe structure type 1 random access configuration for preamble formats0-3. For each subframe, the table shows the subframes allowed for PRACHpreamble transmission.

Proposal to Identify Link-Budget-Limited UE Devices

In one set of embodiments, we propose to have one or more (e.g., one ortwo or three) reserved logical root sequence numbers for thelink-budget-limited devices. The one or more physical root sequencenumbers corresponding to the one or more reserved logical root sequencenumbers are used to generate a special set of Zadoff-Chu sequences, fromwhich a link-budget-limited UE device will randomly select. The specialset may be disjoint from the conventional set of Zadoff-Chu sequencesused by conventional UE devices. (UE devices that are not link budgetlimited may perform PRACH preamble transmission in a conventionalfashion, by selecting from the conventional set.) The number of ZCsequences in the special set may be large enough to satisfy the needs ofthe expected number (or the expected maximum number or a specifiedmaximum number) of link-budget-limited UE devices within the cell.

In some embodiments, the number of sequences reserved for thelink-budget-limited devices may be approximately 12. However, a widevariety of other values or ranges of values are contemplated.

In some embodiments, only a single logical root sequence number isreserved.

In some embodiments, the value of Ncs is selected to be small. Thisfeature may enable the UE to generate the special set of ZC sequences bycyclic shifts using only a single physical root sequence number. (Thenumber of values of shift parameter C_(v) is determined byfloor(N_(ZC)/N_(CS)), as specified in section 5.7.2 of TS 36.211.)

To support the link-budget-limited devices, a small (or smaller) valueof Ncs may be used. (The value Ncs is also referred to herein as “cyclicshift value”). The small value increases the number of cyclic shiftsthat can be applied for a given physical root sequence number.

Now the presence of one of the sequences of the special set willconstitute a particular signature for eNBs to recognizelink-budget-limited devices.

In one set of embodiments, a method 2500 for operating a user equipment(UE) device may include the operations shown in FIG. 25. (The method2500 may also include any subset of the features, elements andembodiments described above.) The method 2500 may be employed tofacilitate successful completion of a random access procedure if (orwhen) the UE device is link budget limited. The operations may beperformed by a processing agent of the UE device, e.g., a processingagent as variously described above.

At 2510, the UE device may receive system information including aconfiguration index for Physical Random Access Channel (PRACH), a cyclicshift value (Ncs) and a logical root number.

At 2520, if the first UE device is link budget limited, the UE devicemay perform a set of operations including operations 2525-2540, asdescribed below.

At 2525, the UE device may compute a first physical root number based onthe logical root number. The first physical root number may be differentfrom a conventional physical root number corresponding to the logicalroot number.

At 2530, the UE device may generate a first set of Zadoff-Chu sequencesbased on the cyclic shift value and one or more physical root numbersincluding the first physical root number.

At 2535, the UE device may randomly select one of the Zadoff-Chusequences of the first set. Methods of making a random selection from aset of objects are well known in the art of signal processing andapplied mathematics.

At 2540, the UE device may transmit a first PRACH subframe that includesrepetitions of the selected Zadoff-Chu sequence. The first PRACHsubframe is transmitted during a first radio frame.

In some embodiments, the first physical root number is a member of areserved set of physical root numbers that has been reserved for useonly by UE devices that are link budget limited.

In some embodiments, the first physical root number is determined basedon a predefined mapping of logical root number to physical root number.The mapping may be agreed upon by the UE device and a base station.

In some embodiments, the first physical root number is computed from thelogical root number using a fixed formula that is known by base stationsof a wireless network to which the UE device is subscribed.

In some embodiments, the number of Zadoff-Chu sequences in said firstset is:

-   -   less than or equal to 32; or    -   less than or equal to 24; or    -   less than or equal to 16; or    -   in the range [9,16]; or    -   in the range [10,14].

In some embodiments, the above-described set of operations also includesthe action of selecting the first radio frame so that its radio framenumber is a multiple of a fixed integer greater than one, wherein thefirst integer is known to base stations of a wireless network to whichto the first UE device is subscribed.

In some embodiments, the above-described set of operations also includestransmitting one or more additional PRACH subframes, wherein each of theone or more additional PRACH subframes includes repetitions of theselected Zadoff-Chu sequence, wherein each of the one or more additionalPRACH subframes occupies a conventionally-allowed subframe of the firstradio frame or a conventionally-allowed subframe of a second radio frameimmediately following the first radio frame, wherein theconventionally-allowed subframes are subframes conventionally allowedbased on the PRACH configuration index as defined in TS 36.211.

In some embodiments, the first set of Zadoff-Chu sequences is disjointfrom the conventional set of 64 Zadoff-Chu sequences as defined by TS36.211 based on the logical sequence number and the cyclic shift value.

In one set of embodiments, a method 2600 for operating a base stationmay include the operations shown in FIG. 26. (The method 2600 may alsoinclude any subset of the features, elements and embodiments describedabove.) The method 2600 may be performed to facilitate a random accessprocedure by a user equipment (UE) device that is link budget limited.The operations may be performed by a processing agent of the basestation, e.g., a processing agent as variously described above.

At 2610, the base station may transmit system information including aconfiguration index for Physical Random Access Channel (PRACH), a cyclicshift value (Ncs) and a logical root number.

At 2615, the base station may receive symbol data over two or moresubframes that are consistent with the PRACH configuration index.

At 2620, the base station may perform a correlation search process todetermine whether the symbol data includes repetitions of any Zadoff-Chusequence from a first set of Zadoff-Chu sequences. The first set ofZadoff-Chu sequences may be determined based on the cyclic shift valueand one or more physical root numbers including a first physical rootnumber, where the first physical root number is different from aconventional physical root number corresponding to the logical rootnumber.

At 2625, in response to the correlation search process determining thatthe symbol data includes repetitions of a particular Zadoff-Chu sequenceof the first set, the base station may store in memory an indicationthat the UE device is link budget limited.

In some embodiments, the two or more subframes occur in one or moreconsecutive radio frames.

In some embodiments, the first physical root number is a member of areserved set of physical root numbers that has been reserved for useonly by UE devices that are link budget limited. In some embodiments,the above-described one or more physical root numbers (of operation2620) are members of a reserved set that has been reserved for use onlyby link-budget-limited UE devices.

In some embodiments, the first physical root number is determined basedon a predefined mapping of logical root number to physical root number,wherein the mapping is agreed between UE device and the base station.

In some embodiments, the number of Zadoff-Chu sequences in said firstset is:

-   -   less than or equal to 32; or    -   less than or equal to 24; or    -   less than or equal to 16; or    -   in the range [9,16]; or    -   in the range [10,14].

In some embodiments, the above-described action of receiving symbol datastarts in first radio frame whose frame number is a multiple of a fixedinteger greater than one, wherein UE devices that are link budgetlimited are configured to start transmitting PRACH information only inradio frames whose frame number is a multiple of the fixed integer.

In some embodiments, the first set of Zadoff-Chu sequences is disjointfrom the conventional set of 64 Zadoff-Chu sequences as defined by TS36.211 based on the logical sequence number and the cyclic shift value.

In some embodiments, the method 2600 may also include: in response tothe indication that the UE device is link budget limited, transmittingone or more messages of a random access procedure to the UE device usinga lower coding rate (or increased redundancy) than used fornon-link-budget limited UE devices.

In some embodiments, the method 2600 may also include: in response tothe indication that the UE device is link budget limited, transmittingdownlink payload data to the UE device using a lower coding rate (orincreased redundancy) than used for non-link-budget-limited UE devices.

In some embodiments, the link-budget-limited UEs use a reserved set ofZC sequences while UE devices that are not link budget limited use aconventional set of ZC sequences for initiating random access (RACH),where the reserved set and the conventional set are disjoint. Thus, thebase station can determine whether a given RACH-initiating UE is linkbudget limited or not by determining the set membership of theparticular ZC sequence contained in the PRACH preamble transmitted bythe given UE. In one embodiment, the base station may be designed (ordirected) to transmit a PRACH configuration with HighSpeed flag set toFALSE. (The base station transmits the PRACH configuration to UE devicesin the cell.) Thus, legacy UE devices and non-link-budget-limited UEdevices may initiate random access (RACH) using the conventional set ofsequences associated with HighSpeed flag=FALSE. (According to the 3GPPspecifications, the conventional set of sequences associated withHighSpeed flag=FALSE is generated using: cyclic shifts C_(v)corresponding to the so-called “unrestricted sets”, and the one or morephysical root sequence numbers specified for the case of unrestrictedsets. However, the link-budget limited UE devices may be configured todisregard the False state of the HighSpeed flag, and initiate randomaccess using the high speed sequences, i.e., the sequencesconventionally associated with HighSpeed flag=TRUE. (According to the3GPP specifications, the high speed sequences are generated using:cyclic shifts C_(v) corresponding to the so-called “restricted sets”,and the one more physical root sequence numbers specified for the caseof restricted sets.) In particular, a given link-budget-limited UE maysignal its link budget limited status to the base station by selectingone of the high speed sequences and initiating the random accessprocedure using the selected sequence. (One or more copies of theselected sequence may be embedded in the PRACH preamble transmitted bythe link-budget-limited UE.) This use of a reserved set as a mechanismto signal link-budget-limited status is agreed upon with the network(NW).

The following is an example of a PRACH configuration that may be used bythe NW:

prach-ConfigInfo { prach-ConfigIndex 5, highSpeedFlag FALSE,zeroCorrelationZoneConfig 12, prach-FreqOffset 4 }

(Note that highSpeedFlag is off.) A wide variety of other configurationsmay be used as well.

Proposal to Improve Range

In some embodiments, the UE may repeat the same selected ZC sequence inone or more consecutive radio frames, and, within each of those radioframes, over all the allowed subframes based on the PRACH configuration.

For example, suppose the eNB is signaling PRACH configuration 7. Thisimplies (as shown in FIG. 24) that any device in the network can send aPRACH preamble on subframe 2 or subframe 7 of any radio frame.

Suppose that a link-budget-limited device needs to send four PRACHsubframes for adequate detectability by the eNB. Under PRACHconfiguration 7, this means that two radios frames will be required forthe link-budget-limited device to send its PRACH preamble, i.e., thefirst two PRACH subframes will be transmitted respectively in subframes2 and 7 of a first radio frame, and the last two PRACH subframes will betransmitted respectively in subframes 2 and 7 of a second radio frameimmediately following the first radio frame.

In order to decode and accumulate the PRACH, the eNB needs to know wherethe PRACH repetition has started.

In some embodiments, in order to simplify the scheme and not make anychange to the SIB2, the link-budget-limited device is constrained tostart, e.g., only on subframe 2 of an even (or odd) radio frame, or moregenerally, only on the first allowed subframe consistent with thesignaled PRACH configuration.

In some embodiments, the link-budget-limited device may start in an evenradio frame (for example, radio frame 12) and then finish in the nextradio frame (radio frame 13). There is no ambiguity in that case for theeNB to decode the PRACH transmitted by the link-budget-limited device.

In order to also reduce the processing load on eNB receiver, oneproposal would be to make the link-budget-limited device send (andstart) its first PRACH subframe only if the radio frame number modulo 4equals 0.

This limits impact on system capacity and load on eNB, but comes at acost of latency for the UE.

Repetition in Single Radio Frame

In some embodiments, the link-budget-limited UE device may transmit thePRACH preamble and one or more temporal repetitions of the PRACHpreamble in a single radio frame. The initial transmission of the PRACHpreamble and the one or more temporal repetitions may occur inconsecutive available subframes of the single radio frame. For example,in PRACH configuration 7, recall that the available subframes are 2 and7. Thus, to allow room for the repetition within a single radio frame,the initial transmission of the PRACH preamble may occur in the firstavailable subframe, i.e., in subframe 2 of the radio frame, and a singlere-transmission of the PRACH preamble may occur in subframe 7 of theradio frame. Thus, the base station may perform accumulation of PRACHtransmissions using the single subframe.

I. Robust PRACH Messaging Format for Link Budget Limited UE Devices

In one set of embodiments, a method for operating a user equipment (UE)device to facilitate a random access procedure may include transmittinga first message including at least three instances of a Zadoff-Chusequence, wherein the first message is transmitted on a physical randomaccess channel (PRACH) within a time-frequency resource space.

In some embodiments, the method may also include performing one or moreretransmissions of the first message, wherein said transmission and saidone or more retransmissions occur according to a pattern of timesdetermined by configuration information transmitted by a first basestation.

In some embodiments, the configuration information determines thepattern of times so that a first set of time-frequency resources usableby the UE device to perform said transmission and said one or moreretransmissions is different from a second set of time-frequencyresources usable by one or more other UE devices to transmitconventional random access preambles, wherein each of the conventionalrandom access preambles includes at most two instances of a Zadoff-Chusequence.

In some embodiments, the method may also include, when a handover of theUE from the first base station to a second base station is beingperformed, receiving a master information block (MIB) from the secondbase station prior to said transmitting the first message, wherein theMIB includes a system frame number associated with the second basestation, wherein the system frame number is used to determine when atime has arrived for performing said transmitting the first message.

In some embodiments, the method may also include, when a handover of theUE from the first base station to a second base station is beingperformed, determining when a time has arrived for performing saidtransmission of the first message based on a system frame numberreceived from the first base station, wherein the system frame number issynchronized between the first base station and the second base station.

In some embodiments, the method may also include, when a handover of theUE from the first base station to a second base station is beingperformed, receiving a radio resource control (RRC) information elementtransmitted by the first base station, wherein the RRC informationelement includes a system frame number associated with the second basestation, wherein the system frame number is used to determine when atime has arrived for performing said transmitting the first message.

In some embodiments, the above-described actions of transmitting thefirst message and said one or more retransmissions are performed inresponse to stored information indicating that the UE is link budgetlimited.

In some embodiments, the action of transmitting the first message andsaid one or more retransmissions are performed in response to the UEdetermining that the UE is operating in a link-budget-limited condition.

In some embodiments, the method may also include, prior to saidtransmitting the first message, receiving the configuration informationtransmitted by the base station.

In some embodiments, the configuration information identifies thepattern of times from a predefined set of timing patterns, wherein eachof the timing patterns.

In some embodiments, the first message includes a plurality ofsub-carriers for conveying said at least three instances of theZadoff-Chu sequence, wherein a spacing of the subcarriers is greaterthan 1.25 kHz.

In some embodiments, the first message spans more than one subframe.

In some embodiments, the method may also include receiving a secondmessage transmitted by a base station, wherein the second message istransmitted by the base station in response to the base stationsuccessfully decoding the first message.

In some embodiments, the second message is transmitted by the basestation two or more times and/or with lower coding rate.

In some embodiments, the second message is transmitted by the basestation with a coding rate lower than conventional random accessresponse messages.

In some embodiments, the method may also include transmitting a thirdmessage to the base station in response to successfully decoding thesecond message from the base station, wherein the third message istransmitted (a) with lower coding data rate than conventional PUSCHmessages and/or (b) repeatedly in time.

In one set of embodiments, a method for operating a user equipment (UE)device may include transmitting a physical random access channel (PRACH)according to any one of the enhanced formats described herein, whereinsaid transmission of the PRACH according to said one of the enhancedformat indicates to a base station (and/or to the network) that the UEdevice is link budget limited.

In some embodiments, the base station modifies its resource assignmentin DL and grant in UL such that decoding of UL and DL messages aresuccessful.

In some embodiments, the PRACH includes two or more segments spanningthe same interval in time but occupying different intervals infrequency.

In one set of embodiments, a method for operating a base station mayinclude the following operations.

The method may include transmitting first configuration information forone or more link-budget-limited user equipment (UE) devices, whereineach of the link-budget-limited UE devices is configured to transmit arandom access preamble and perform one or more retransmissions of therandom access preamble, wherein the random access preamble includes oneor more instances of a Zadoff-Chu sequence, wherein the firstconfiguration information indicates a pattern of times for saidtransmission and said one or more retransmissions of the random accesspreamble.

The method may also include receiving said transmission of the randomaccess preamble from a first of the one or more UE devices to obtain afirst data record,

The method may also include receiving said one or more retransmissionsof the random access preamble from the first UE device to obtain one ormore additional data records.

The method may also include decoding the random access preamble based onthe first data record and the one or more additional data records.

In some embodiments, the method may also include transmitting secondconfiguration information for one or more UE devices that are not linkbudget limited, wherein each of the UE devices that are not link budgetlimited is configured to transmit a second random access preamble basedon timing identified by the second configuration information, whereinthe second random access preamble includes at most two instances of aZadoff-Chu sequence.

In some embodiments, the first configuration information and the secondconfiguration information are determined by the base station so that afirst set of time-frequency resources usable by the first UE device toperform said transmission and said one or more retransmissions of therandom access preamble is different from a second set of time-frequencyresources usable by the one or more UE devices that are not link budgetlimited to transmit the second random access preambles.

In some embodiments, the method may also include, in response todecoding the random access preamble, transmitting a random accessresponse to the first UE device, wherein the random access response istransmitted (a) with lower coding rate than conventional random accessresponses and/or (b) using a plurality of repetitions in time.

In some embodiments, the method may also include receiving a messagefrom the first UE device, wherein the first UE device transmits themessage after receiving the random access response, wherein the messageis transmitted with coding rate lower than normal PUSCH messages and/orwith a plurality of repetitions in time.

In some embodiments, the first configuration information identifies thepattern of times from a predetermined set of time patterns.

In some embodiments, the random access preamble includes at least threeinstances of the Zadoff-Chu sequence.

In some embodiments, the random access preamble includes a plurality ofsub-carriers for conveying said at least three instances of theZadoff-Chu sequence, wherein a spacing of the subcarriers is greaterthan 1.25 kHz.

In some embodiments, the random access preamble spans more than one subframe.

In one set of embodiments, a method for operating a base station mayinclude the following operations. The operations may be performed inorder to facilitate random access by one or more link-budget-limiteduser equipment (UE) devices. Each of the link-budget-limited UE devicesis configured to transmit a random access preamble and perform one ormore retransmissions of the random access preamble, wherein the randomaccess preamble includes one or more instances of a Zadoff-Chu sequence(e.g., a Zadoff-Chu sequence randomly selected by thelink-budget-limited UE device). The base station and the one or morelink-budget-limited UE devices may have previously agreed upon a patternof times (and/or other configuration features such as frequency hoppingpattern) for said transmission and said one or more retransmissions ofthe random access preamble. Thus, the pattern of times (and/or otherconfiguration features) does not need to be signaled to the one or morelink-budget-limited UE devices.

The operations may include receiving said transmission of the randomaccess preamble from a first of the one or more UE devices to obtain afirst data record.

The operations may also include receiving said one or moreretransmissions of the random access preamble from the first UE deviceto obtain one or more additional data records.

The operations may also include decoding the random access preamblebased on the first data record and the one or more additional datarecords.

II. Signaling by Sequence Set Selection, for Link Budget Limited UEDevices

In one set of embodiments, a method for operating a user equipment (UE)device to facilitate a random access procedure may include: selecting aset from a plurality of sets of Zadoff-Chu sequences based on ameasurement of Doppler shift magnitude of UE relative to a base station,wherein identity of the selected set among the plurality of sets isusable by a base station to determine a correlation accumulation method;and performing two or more transmissions of a first message, wherein thefirst message includes one or more instances of a particular Zadoff-Chusequence chosen from the selected set.

In some embodiments, the two or more transmissions are performed withfrequency hopping over a plurality of time intervals, wherein differentones of the sets are associated with different patterns of frequencyhopping.

In some embodiments, the two or more transmissions are performedaccording to one of a plurality of possible repetition patterns in time,wherein different ones of the sets are associated with different ones ofthe repetitions patterns in time.

In some embodiments, the correlation accumulation method is selectedfrom a complex-valued accumulation method and an energy accumulationmethod.

In one set of embodiments, a method for operating a user equipment (UE)device to facilitate a random access procedure may include: selecting aset from a plurality of sets based on a measurement of Doppler shiftmagnitude of UE relative to a base station, wherein each of the setsincludes a plurality of Zadoff-Chu sequences, wherein different ones ofthe sets have been assigned to different ranges of Doppler shiftmagnitude; and performing two or more transmissions of a first message,wherein the first message includes one or more instances of a particularZadoff-Chu sequence chosen from the selected set.

In some embodiments, the base station is configured to: (a) receivesymbol data in response to the two or more transmissions of the firstmessage; (b) perform correlation processing on the symbol data to obtaininformation identifying the particular Zadoff-Chu sequence andinformation identifying the selected set among the plurality of sets;(c) select a correlation accumulation method from a complex-valuedaccumulation method and an energy accumulation method based on theinformation identifying the selected set; and (d) accumulate two or morecorrelation sequences according to the selected correlation accumulationmethod, wherein each of the two or more correlation sequences isgenerated by correlation of a respective portion of the symbol data withthe particular Zadoff-Chu sequence, wherein each of the portions of thesymbol data corresponds to a respective instance of the particularZadoff-Chu sequence in one of the two or more transmissions.

In some embodiments, each of the two or more transmissions occurs in adifferent time interval, wherein a first of the transmissions in a firsttime interval occupies a first set of frequency resources, wherein asecond of the transmissions in a second time interval occupies a secondset of frequency resources different from the first set of frequencyresources.

In some embodiments, the two or more transmissions respectively occupytwo or more distinct time intervals, wherein frequency resources used toperform the two or more transmissions change from one the time intervalsto the next according to a particular one of a plurality of frequencyhopping patterns, wherein each of the plurality frequency hoppingpatterns is associated with a respective one of the plurality of sets.

In some embodiments, the base station is configured to: (a) receivesymbol data in response to the two or more transmissions of the firstmessage; (b) perform correlation processing on subsets of the symboldata, wherein each of the subsets of the symbol data corresponds to arespective one of the frequency hopping patterns, wherein thecorrelation processing determines information identifying the particularZadoff-Chu sequence and information identifying the selected set amongthe plurality of sets of Zadoff-Chu sequences; (c) accumulate two ormore correlation sequences generated by correlating two or morerespective portions of a particular subset of the symbol data with theparticular Zadoff-Chu sequence, wherein the particular subset of thesymbol data is chosen based on the information identifying the selectedset of Zadoff-Chu sequences, wherein each of the two or more portions ofthe particular subset corresponds to a respective instance of theparticular Zadoff-Chu sequence in one of the two or more transmissionsof the first message.

In some embodiments, the two or more transmissions are performedaccording to one of a plurality of repetition patterns in time, whereineach of the repetition patterns in time is associated with a respectiveone of the sets of Zadoff-Chu sequences.

In some embodiments, the base station is configured to: (a) receivesymbol data in response to the two or more transmissions of the firstmessage; (b) perform correlation processing on subsets of the symboldata, wherein each of the subsets corresponds to a respective one of therepetitions patterns in time, wherein the correlation processingdetermines information identifying the particular Zadoff-Chu sequenceand information identifying the selected set among the plurality of setsof Zadoff-Chu sequences; and (c) accumulate two or more correlationsequences to obtain an accumulated correlation sequence, wherein the twoor more correlation sequences are generated by correlating two or morerespective portions of a particular subset of the symbol data with theparticular Zadoff-Chu sequence, wherein the particular subset of thesymbol data is chosen based on the information identifying the selectedset of Zadoff-Chu sequences, wherein each of the two or more respectiveportions corresponds to a respective instance of the particularZadoff-Chu sequence in one of the two or more transmissions of the firstmessage.

In one set of embodiments, a method for operating a base station (tofacilitate a random access procedure by a user equipment device) mayinclude the following operations.

The method may include receiving symbol data in response to two or moretransmissions of a first message from the UE device, wherein the UEdevice performs the two or more transmissions using a particularZadoff-Chu sequence chosen from one of a plurality of sets of Zadoff-Chusequences.

The method may also include performing correlation processing on thesymbol data to identify said one set to which the particular Zadoff-Chusequence belongs.

The method may also include accumulating correlation data records usingan accumulation method, wherein the accumulation method is selected froma complex-valued accumulation method or an energy accumulation methodbased on the identity of said set.

In some embodiments, the UE device performs the two or moretransmissions using frequency hopping over a plurality of timeintervals, wherein different ones of the sets are associated withdifferent patterns of frequency hopping. In these embodiments, the basestation operating method may also include determining the frequencyhopping pattern based on the identity of said set.

In some embodiments, the UE device performs the two or moretransmissions according to one or a plurality of possible repetitionspatterns in time, wherein different ones of the sets are associated withdifferent repetition patterns in time. In these embodiments, the basestation operating method may also include determining the repetitionpattern based on the identity of said set.

In some embodiments, the correlation accumulation method is selectedfrom a complex-valued accumulation method and an energy accumulationmethod.

In one set of embodiments, a method for operating a base station (tofacilitate a random access procedure by a user equipment device) mayinclude the following operations.

The method may include receiving symbol data in response to two or moretransmissions of a first message from the UE device, wherein the firstmessage includes one or more instances of a particular Zadoff-Chusequence, wherein the particular Zadoff-Chu sequence has been chosen bythe UE device from a selected one of a plurality of sets of Zadoff-Chusequences, wherein each of the sets corresponds to a different range ofmagnitude of Doppler shift of the UE device relative to the basestation.

The method may also include performing correlation processing on thesymbol data to determine information identifying the particularZadoff-Chu sequence and information identifying the selected set amongthe plurality of sets.

The method may also include selecting a correlation accumulation methodfrom a complex-valued accumulation method and an energy accumulationmethod based on the information identifying the selected set.

The method may also include accumulating two or more correlationsequences according to the selected correlation accumulation method,wherein each of the two or more correlation sequences is generated bycorrelation of a respective portion of the symbol data with theparticular Zadoff-Chu sequence, wherein each of the portions of thesymbol data corresponds to a respective instance of the particularZadoff-Chu sequence in one of the two or more transmissions.

In some embodiments, each of the two or more transmissions occurs in adifferent time interval, wherein a first of the transmissions in a firsttime interval occupies a first set of frequency resources, wherein asecond of the transmissions in a second time interval occupies a secondset of frequency resources different from the first set of frequencyresources.

In some embodiments, the two or more transmissions respectively occupytwo or more distinct time intervals, wherein frequency resources used toperform the two or more transmissions change from one the time intervalsto the next according to a particular one of a plurality of frequencyhopping patterns, wherein each of the plurality frequency hoppingpatterns is associated with a respective one of the plurality of sets.

In some embodiments, the base station operating method may also include:(a) receiving symbol data in response to the two or more transmissionsof the first message; (b) performing correlation processing on subsetsof the symbol data, wherein each of the subsets of the symbol datacorresponds to a respective one of the frequency hopping patterns,wherein the correlation processing determines information identifyingthe particular Zadoff-Chu sequence and information identifying theselected set among the plurality of sets of Zadoff-Chu sequences; and(c) accumulating two or more correlation sequences generated bycorrelating two or more respective portions of a particular subset ofthe symbol data with the particular Zadoff-Chu sequence, wherein theparticular subset of the symbol data is chosen based on the informationidentifying the selected set of Zadoff-Chu sequences, wherein each ofthe two or more portions of the particular subset corresponds to arespective instance of the particular Zadoff-Chu sequence in one of thetwo or more transmissions of the first message.

In some embodiments, the two or more transmissions are performedaccording to one of a plurality of repetition patterns in time, whereineach of the repetition patterns in time is associated with a respectiveone of the sets of Zadoff-Chu sequences.

In some embodiments, the base station operating method may also include:(a) receiving symbol data in response to the two or more transmissionsof the first message; (b) performing correlation processing on subsetsof the symbol data, wherein each of the subsets corresponds to arespective one of the repetitions patterns in time, wherein thecorrelation processing determines information identifying the particularZadoff-Chu sequence and information identifying the selected set amongthe plurality of sets of Zadoff-Chu sequences; and (c) accumulating twoor more correlation sequences to obtain an accumulated correlationsequence, wherein the two or more correlation sequences are generated bycorrelating two or more respective portions of a particular subset ofthe symbol data with the particular Zadoff-Chu sequence, wherein theparticular subset of the symbol data is chosen based on the informationidentifying the selected set of Zadoff-Chu sequences, wherein each ofthe two or more respective portions corresponds to a respective instanceof the particular Zadoff-Chu sequence in one of the two or moretransmissions of the first message.

In some embodiments, the first message includes two instances of theparticular Zadoff-Chu sequence.

III. Repeated PRACH Instances Transmitted Over Consecutive Subframes

In one set of embodiments, a method for operating a first user equipmentdevice (to facilitate a random access procedure when the first UE deviceis link budget limited) may include transmitting a plurality ofinstances of a Physical Random Access Channel (PRACH) over a pluralityof consecutive subframes to a base station, with each of the consecutivesubframes including a corresponding one of the PRACH instances.

In some embodiments, resource blocks used by the first UE device totransmit a first of the PRACH instances in a first of the consecutivesubframes are disjoint from resource blocks used by a second UE deviceto transmit a conventional PRACH subframe, wherein the second UE deviceis not link budget limited.

In some embodiments, resource blocks used by the first UE device totransmit a first of the PRACH instances in a first of the consecutivesubframes at least partially overlap with resource blocks used by asecond UE device to transmit a conventional PRACH subframe, wherein thesecond UE device is not link budget limited, wherein the first UE deviceand the second UE device are each configured to randomly select acorresponding ZC root for PRACH transmission. (Thus, the independentlyselected ZC roots are likely to be sufficiently orthogonal for uniqueidentification at the base station.)

In some embodiments, the method also includes receiving systeminformation (e.g., as part of SIB2) that indicates the number of saidconsecutive subframes.

In some embodiments, the number of said successive subframes is fixed,and known by the first UE device and the base station.

In some embodiments, wherein resource blocks used by the first UE deviceto transmit a PRACH instance hop in the frequency domain from one of theconsecutive subframes to the next.

In some embodiments, a hopping pattern according to which the resourceblocks hop in the frequency domain is fixed and known by the first UEdevice and the base station.

In some embodiments, the method may also include receiving systeminformation (e.g., as part of SIB2) identifying a hopping pattern to beused to perform said hopping in the frequency domain.

In one set of embodiments, a method for operating a base station (tofacilitate a random access procedure by a user equipment device) mayinclude: receiving symbol data in response to a transmission of aplurality of instances of a PRACH by the UE device, wherein theplurality of PRACH instances are transmitted over a plurality ofconsecutive subframes, wherein each of the plurality of consecutivesubframes contains a corresponding one of the PRACH instances; andperforming correlation processing on the symbol data to determine whichZadoff-Chu (ZC) sequence from a set of available ZC sequences isincluded in the plurality of PRACH instances, wherein said correlationprocessing accumulates correlation data over the plurality ofconsecutive subframes.

In some embodiments, resource blocks used by the first UE device totransmit a first of the PRACH instances in a first of the consecutivesubframes are disjoint from resource blocks used by a second UE deviceto transmit a conventional PRACH subframe, wherein the second UE deviceis not link budget limited.

In some embodiments, resource blocks used by the first UE device totransmit a first of the PRACH instances in a first of the consecutivesubframes at least partially overlap with resource blocks used by asecond UE device to transmit a conventional PRACH subframe, wherein thesecond UE device is not link budget limited, wherein the first UE deviceand the second UE device are each configured to randomly select acorresponding ZC root for PRACH transmission.

IV. Transmission of PRACH Instances after Conventional PRACH Preamble

In one set of embodiments, a method for operating a first user equipment(UE) device (to facilitate a random access procedure) may include thefollowing operations.

If the first UE device is link budget limited, the first UE device mayperform operations including: transmitting a first set of one or moreinstances of a Physical Random Access Channel (PRACH) respectively overa first set of one or more consecutive subframes, wherein saidtransmitting the first set of one or more PRACH instances is performedaccording to a conventional format for transmission of PRACH; andtransmitting a second set of one or more instances of the PRACHrespectively over a second set of one or more consecutive subframesstarting immediately after a last subframe of the first set of one ormore subframes, wherein each of the one or more PRACH instances of thefirst set and each of the one or more PRACH instances of the second setuse the same Zadoff-Chu sequence.

In some embodiments, the method may also include, prior to saidtransmitting the first set of one or more PRACH instances, receivingsystem information (e.g., in SIB2) from a base station, wherein thesystem information indicates at least the conventional format. (The“conventional format” may, e.g., be a format specified by 3GPP TS36.211.)

In some embodiments, the conventional format is a fixed format known toa base station serving the UE device.

In some embodiments, the conventional format corresponds to PRACH format0 of 3GPP TS 36.211, wherein the first set of one or more subframesincludes only one subframe.

In some embodiments, the conventional format corresponds to PRACH format2 of 3GPP TS 36.211, wherein the first set of one or more subframesincludes exactly two subframes.

In some embodiments, a PRACH configuration (e.g., number ofPRACH-containing resource blocks, number of ZC sequence repetitions, ZCsequence length) for each subframe of the first set and for eachsubframe of the second set is identical.

In one set of embodiments, a method for operating a first user equipmentdevice (to facilitate a random access procedure) may include thefollowing actions. If the first UE device is link budget limited, thefirst UE device may perform operations including: transmitting a firstset of one or more consecutive subframes including a first PhysicalRandom Access Channel (PRACH), wherein the first PRACH is transmittedaccording to a conventional format for PRACH transmission; andtransmitting a second set of one or more consecutive subframescontaining one or more repetitions of the first PRACH, wherein thesecond set of one or more subframes starts immediately after a lastsubframe of the first set of one or more subframes, wherein each of theone or more PRACH repetitions uses the same Zadoff-Chu sequence as thefirst PRACH.

In one set of embodiments, a method for operating a base station (tofacilitate a random access procedure by a user equipment device) mayinclude the following operations.

The method may include receiving a first symbol data set in response toa first transmission by the UE device, wherein the first transmissionincludes a first set of one or more instances of a Physical RandomAccess Channel (PRACH) respectively over a first set of one or moreconsecutive subframes, wherein said first transmission is performedaccording to a conventional format for transmission of PRACH.

The method may also include receiving a second symbol data set inresponse to a subsequent transmission by the UE device, wherein thesubsequent transmission includes a second set of one or more consecutivesubframes starting immediately after a last subframe of the first set ofone or more subframes.

The method may also include performing correlation processing on a unionof the first symbol data set and the second symbol data set to determineif the second set of one or more consecutive subframes contains one ormore PRACH instances in addition to the first set of one or more PRACHinstances, wherein the one or more additional PRACH instances, ifpresent, are assumed to use to the same ZC sequence as the one or morePRACH instances of the first set.

The method may also include, in response to determining that the secondset of one or more consecutive subframes contains one or more PRACHinstances in addition to the first set of one or more PRACH instances,storing in memory an indication that the UE device is link budgetlimited.

In some embodiments, the method may also include, prior to theabove-described action of receiving the first symbol data set,transmitting system information that indicates at least the conventionalformat.

In some embodiments, the conventional format is a fixed format known tothe base station.

In some embodiments, the method also includes, in response to theindication that the UE device is link budget limited, transmitting oneor more messages of a random access procedure to the UE device using alower coding rate (or increased redundancy) than used fornon-link-budget limited UE devices.

In some embodiments, the method also includes, in response to theindication that the UE device is link budget limited, transmittingdownlink payload data to the UE device using a lower coding rate (orincreased redundancy) than used for non-link-budget limited UE devices.

In one set of embodiments, a method for operating a base station (tofacilitate a random access procedure by a user equipment device) mayinclude the following operations.

The method may include receiving a first symbol data set in response toa first transmission by the UE device, wherein the first transmission isa transmission of a first set of one or more consecutive subframesincluding a first Physical Random Access Channel (PRACH), wherein saidfirst PRACH is transmitted according to a conventional format for PRACHtransmission.

The method may also include receiving a second symbol data set inresponse to a subsequent transmission by the UE device, wherein thesubsequent transmission is a transmission of a second set of one or moreconsecutive subframes, wherein the second set of one or more consecutivesubframes starts immediately after a last subframe of the first set ofone or more subframes.

The method may also include performing correlation processing on a unionof the first symbol data set and the second symbol data set to determineif the second set of one or more consecutive subframes contains one ormore repetitions of the first PRACH, wherein the one or more repetitionsof the first PRACH, if present, are assumed to use to the sameZadoff-Chu sequence as the first PRACH.

The method may also include, in response to determining that the secondset of one or more consecutive subframes contains one or morerepetitions of the first PRACH, storing in memory an indication that theUE device is link budget limited.

V. Reserved Logical Root Sequence Numbers for the Link-Budget-LimitedDevices

In one set of embodiments, a method for operating a first user equipmentdevice (to facilitate a random access procedure) may include thefollowing actions.

The method may include receiving system information including aconfiguration index for Physical Random Access Channel (PRACH), a cyclicshift value (Ncs) and a logical root number.

If the first UE device is link budget limited, the method may alsoinclude performing operations including: (a) computing a first physicalroot number based on the logical root number, wherein the first physicalroot number is different from a conventional physical root numbercorresponding to the logical root number; (b) generating a first set ofZadoff-Chu sequences based on the cyclic shift value and one or morephysical root numbers including the first physical root number; (c)randomly selecting one of the Zadoff-Chu sequences of the first set; and(d) transmitting a first PRACH subframe that includes repetitions of theselected Zadoff-Chu sequence, wherein the first PRACH subframe istransmitted during a first radio frame.

In some embodiments, the first physical root number is a member of areserved set of physical root numbers that has been reserved for useonly by UE devices that are link budget limited.

In some embodiments, the first physical root number is determined basedon a predefined mapping of logical root number to physical root number,wherein the mapping is agreed between UE device and a base station.

In some embodiments, the first physical root number is computed from thelogical root number using a fixed formula that is known by base stationsof a wireless network to which the UE device is subscribed.

In some embodiments, the number of Zadoff-Chu sequences in said firstset is: less than or equal to 32; or less than or equal to 24; or lessthan or equal to 16; or in the range [9,16]; or in the range [10,14].

In some embodiments, the above-described operations may also includeselecting the first radio frame so that its radio frame number is amultiple of a fixed integer greater than one, wherein the first integeris known to base stations of a wireless network to which to the first UEdevice is subscribed.

In some embodiments, the operations also include transmitting one ormore additional PRACH subframes, wherein each of the one or moreadditional PRACH subframes includes repetitions of the selectedZadoff-Chu sequence, wherein each of the one or more additional PRACHsubframes occupies a conventionally-allowed subframe of the first radioframe or a conventionally-allowed subframe of a second radio frameimmediately following the first radio frame, wherein theconventionally-allowed subframes are subframes conventionally allowedbased on the PRACH configuration index as defined in TS 36.211.

In some embodiments, the first set of Zadoff-Chu sequences is disjointfrom the conventional set of 64 Zadoff-Chu sequences as defined by TS36.211 based on the logical sequence number and the cyclic shift value.

In one set of embodiments, a method for operating a base station (tofacilitate a random access procedure by a user equipment device) mayinclude the following operations.

The method may include transmitting system information including aconfiguration index for Physical Random Access Channel (PRACH), a cyclicshift value (Ncs) and a logical root number.

The method may also include receiving symbol data over two or moresubframes that are consistent with the PRACH configuration index.

The method may also include performing a correlation search process todetermine whether the symbol data includes repetitions of any Zadoff-Chusequence from a first set of Zadoff-Chu sequences, wherein the first setof Zadoff-Chu sequences is determined based on the cyclic shift valueand one or more physical root numbers including a first physical rootnumber, wherein the first physical root number is different from aconventional physical root number corresponding to the logical rootnumber.

The method may also include, in response to said correlation searchprocess determining that the symbol data includes repetitions of aparticular Zadoff-Chu sequence of the first set, storing in memory anindication that the UE device is link budget limited.

In some embodiments, the two or more subframes occur in one or moreconsecutive radio frames.

In some embodiments, the first physical root number is a member of areserved set of physical root numbers that has been reserved for useonly by UE devices that are link budget limited.

In some embodiments, the first physical root number is determined basedon a predefined mapping of logical root number to physical root number,wherein the mapping is agreed between UE device and the base station.

In some embodiments, the number of Zadoff-Chu sequences in said firstset is: less than or equal to 32; or less than or equal to 24; or lessthan or equal to 16; or in the range [9,16]; or in the range [10,14].

In some embodiments, wherein the above-described action of receivingsymbol data starts in first radio frame whose frame number is a multipleof a fixed integer greater than one, wherein UE devices that are linkbudget limited are configured to start transmitting PRACH informationonly in radio frames whose frame number is a multiple of the fixedinteger.

In some embodiments, the first set of Zadoff-Chu sequences is disjointfrom the conventional set of 64 Zadoff-Chu sequences as defined by TS36.211 based on the logical sequence number and the cyclic shift value.

In some embodiments, the method may also include, in response to theindication that the UE device is link budget limited, transmitting oneor more messages of a random access procedure to the UE device using alower coding rate (or increased redundancy) than used fornon-link-budget limited UE devices.

In some embodiments, the method may also include, in response to theindication that the UE device is link budget limited, transmittingdownlink payload data to the UE device using a lower coding rate (orincreased redundancy) than used for non-link-budget-limited UE devices.

Embodiments of the present invention may be realized in any of variousforms. For example, in some embodiments, the present invention may berealized as a computer-implemented method, a non-transitorycomputer-readable memory medium, or a computer system. In otherembodiments, the present invention may be realized using one or morecustom-designed hardware devices such as ASICs. In other embodiments,the present invention may be realized using one or more programmablehardware elements such as FPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE or a base station) may beconfigured to include a processor (or a set of processors) and a memorymedium, where the memory medium stores program instructions, where theprocessor is configured to read and execute the program instructionsfrom the memory medium, where the program instructions are executable toimplement any of the various method embodiments described herein (or,any combination of the method embodiments described herein, or, anysubset of any of the method embodiments described herein, or, anycombination of such subsets). The device may be realized in any ofvarious forms.

In some embodiments, an integrated circuit may be configured to performany of the various method embodiments described herein (or, anycombination of the method embodiments described herein, or, any subsetof any of the method embodiments described herein, or, any combinationof such subsets). The integrated circuit may be realized in any ofvarious forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A method for operating a base station, the methodcomprising: perform operations in order to facilitate random access byone or more link-budget-limited user equipment (UE) devices, whereineach of the link-budget-limited UE devices is configured to transmit arandom access preamble and perform one or more retransmissions of therandom access preamble, wherein the random access preamble includes oneor more instances of a Zadoff-Chu sequence, wherein the operationsinclude: receiving said transmission of the random access preamble froma first of the one or more UE devices to obtain a first data record;receiving said one or more retransmissions of the random access preamblefrom the first UE device to obtain one or more additional data records;decoding the random access preamble based on the first data record andthe one or more additional data records.
 2. The method of claim 1,further comprising: transmitting first configuration information for theone or more link-budget-limited user equipment (UE) devices, wherein thefirst configuration information indicates a pattern of times for saidtransmission and said one or more retransmissions of the random accesspreamble; and/or transmitting second configuration information for oneor more UE devices that are not link budget limited, wherein each of theUE devices that are not link budget limited is configured to transmit asecond random access preamble based on timing identified by the secondconfiguration information, wherein the second random access preambleincludes at most two instances of a Zadoff-Chu sequence.
 3. The methodof claim 1, further comprising: in response to decoding the randomaccess preamble, transmitting a random access response to the first UEdevice, wherein the random access response is transmitted (a) with lowercoding rate than conventional random access responses and/or (b) using aplurality of repetitions in time.
 4. A method for operating a first userequipment (UE) device to facilitate a random access procedure when thefirst UE device is link budget limited, the method comprising:transmitting a plurality of instances of a Physical Random AccessChannel (PRACH) over a plurality of consecutive subframes to a basestation, with each of the consecutive subframes including acorresponding one of the PRACH instances; wherein resource blocks usedby the first UE device to transmit a first of the PRACH instances in afirst of the consecutive subframes at least partially overlap withresource blocks used by a second UE device to transmit a conventionalPRACH subframe, wherein the second UE device is not link budget limited,wherein the first UE device and the second UE device are each configuredto randomly select a corresponding Zadoff-Chu (ZC) root for PRACHtransmission.
 5. The method of claim 4, wherein resource blocks used bythe first UE device to transmit a PRACH instance hop in a frequencydomain from one of the consecutive subframes to the next.
 6. A methodfor operating a base station to facilitate a random access procedure bya user equipment (UE) device, the method comprising: receiving symboldata in response to a transmission of a plurality of instances of aPRACH by the UE device, wherein the plurality of PRACH instances aretransmitted over a plurality of consecutive subframes, wherein each ofthe plurality of consecutive subframes contains a corresponding one ofthe PRACH instances; performing correlation processing on the symboldata to determine which Zadoff-Chu (ZC) sequence from a set of availableZC sequences is included in the plurality of PRACH instances, whereinsaid correlation processing accumulates correlation data over theplurality of consecutive subframes.
 7. The method of claim 6, whereinresource blocks used by the UE device to transmit a first of the PRACHinstances in a first of the consecutive subframes are disjoint fromresource blocks used by a second UE device to transmit a conventionalPRACH subframe, wherein the second UE device is not link budget limited.8. The method of claim 6, wherein resource blocks used by the UE deviceto transmit a first of the PRACH instances in a first of the consecutivesubframes at least partially overlap with resource blocks used by asecond UE device to transmit a conventional PRACH subframe, wherein thesecond UE device is not link budget limited, wherein the first UE deviceand the second UE device are each configured to randomly select acorresponding ZC root for PRACH transmission.
 9. A method for operatinga first user equipment (UE) device to facilitate a random accessprocedure, the method comprising: when the first UE device is linkbudget limited, performing operations including: transmitting a firstset of one or more instances of a Physical Random Access Channel (PRACH)respectively over a first set of one or more consecutive subframes,wherein said transmitting the first set of one or more PRACH instancesis performed according to a conventional format for transmission ofPRACH; transmitting a second set of one or more instances of the PRACHrespectively over a second set of one or more consecutive subframesstarting immediately after a last subframe of the first set of one ormore subframes, wherein each of the one or more PRACH instances of thefirst set and each of the one or more PRACH instances of the second setuse the same Zadoff-Chu sequence.
 10. The method of claim 9, furthercomprising: prior to said transmitting the first set of one or morePRACH instances, receiving system information from a base station,wherein the system information indicates at least the conventionalformat.
 11. The method of claim 9, wherein a PRACH configuration foreach subframe of the first set and for each subframe of the second setis identical.
 12. A method for operating a base station to facilitate arandom access procedure by a user equipment (UE) device, the methodcomprising: receiving a first symbol data set in response to a firsttransmission by the UE device, wherein the first transmission includes afirst set of one or more instances of a Physical Random Access Channel(PRACH) respectively over a first set of one or more consecutivesubframes, wherein said first transmission is performed according to aconventional format for transmission of PRACH; receiving a second symboldata set in response to a subsequent transmission by the UE device,wherein the subsequent transmission includes a second set of one or moreconsecutive subframes starting immediately after a last subframe of thefirst set of one or more subframes; performing correlation processing ona union of the first symbol data set and the second symbol data set todetermine if the second set of one or more consecutive subframescontains one or more PRACH instances in addition to the first set of oneor more PRACH instances, wherein the one or more additional PRACHinstances, if present, are assumed to use to the same ZC sequence as theone or more PRACH instances of the first set; and in response todetermining that the second set of one or more consecutive subframescontains one or more PRACH instances in addition to the first set of oneor more PRACH instances, storing in memory an indication that the UEdevice is link budget limited.
 13. The method of claim 12, furthercomprising: prior to said receiving the first symbol data set,transmitting system information that indicates at least the conventionalformat.
 14. The method of claim 12, wherein the conventional format is afixed format known to the base station.
 15. The method of claim 12,further comprising: in response to the indication that the UE device islink budget limited, transmitting one or more messages of a randomaccess procedure to the UE device using a lower coding rate than usedfor non-link-budget limited UE devices.
 16. The method of claim 12,further comprising: in response to the indication that the UE device islink budget limited, transmitting downlink payload data to the UE deviceusing a lower coding rate than used for non-link-budget limited UEdevices.
 17. A method for operating a first user equipment (UE) deviceto facilitate a random access procedure, the method comprising:receiving system information including a configuration index forPhysical Random Access Channel (PRACH), a cyclic shift value (Ncs) and alogical root number; when the first UE device is link budget limited,performing operations including: computing a first physical root numberbased on the logical root number, wherein the first physical root numberis different from a conventional physical root number corresponding tothe logical root number; generating a first set of Zadoff-Chu sequencesbased on the cyclic shift value and one or more physical root numbersincluding the first physical root number; randomly selecting one of theZadoff-Chu sequences of the first set; transmitting a first PRACHsubframe that includes repetitions of the selected Zadoff-Chu sequence,wherein the first PRACH subframe is transmitted during a first radioframe.
 18. The method of claim 17, wherein the first physical rootnumber is a member of a reserved set of physical root numbers that hasbeen reserved for use only by UE devices that are link budget limited.19. The method of claim 17, wherein the first physical root number isdetermined based on a predefined mapping of logical root number tophysical root number, wherein the mapping is agreed between UE deviceand a base station.
 20. The method of claim 17, wherein the firstphysical root number is computed from the logical root number using afixed formula that is known by base stations of a wireless network towhich the UE device is subscribed.
 21. A method for operating a basestation to facilitate a random access procedure by a user equipment (UE)device, the method comprising: transmitting system information includinga configuration index for Physical Random Access Channel (PRACH), acyclic shift value (Ncs) and a logical root number; receiving symboldata over two or more subframes that are consistent with the PRACHconfiguration index; performing a correlation search process todetermine whether the symbol data includes repetitions of any Zadoff-Chusequence from a first set of Zadoff-Chu sequences, wherein the first setof Zadoff-Chu sequences is determined based on the cyclic shift valueand one or more physical root numbers including a first physical rootnumber, wherein the first physical root number is different from aconventional physical root number corresponding to the logical rootnumber; in response to said correlation search process determining thatthe symbol data includes repetitions of a particular Zadoff-Chu sequenceof the first set, storing in memory an indication that the UE device islink budget limited.
 22. The method of claim 21, wherein the two or moresubframes occur in one or more consecutive radio frames.
 23. The methodof claim 21, wherein said receiving symbol data starts in first radioframe whose frame number is a multiple of a fixed integer greater thanone, wherein UE devices that are link budget limited are configured tostart transmitting PRACH information only in radio frames whose framenumber is a multiple of the fixed integer.
 24. The method of claim 21,wherein the first set of Zadoff-Chu sequences is disjoint from theconventional set of Zadoff-Chu sequences as defined by TS 36.211 basedon the logical sequence number and the cyclic shift value.
 25. Anapparatus configured for inclusion in a link budget limited userequipment (UE) device, comprising: one or more processing elements,wherein the one or more processing elements are configured to: transmita first set of one or more instances of a Physical Random Access Channel(PRACH) respectively over a first set of one or more consecutivesubframes, wherein said transmitting the first set of one or more PRACHinstances is performed according to a conventional format fortransmission of PRACH; and transmit a second set of one or moreinstances of the PRACH respectively over a second set of one or moreconsecutive subframes starting immediately after a last subframe of thefirst set of one or more subframes, wherein each of the one or morePRACH instances of the first set and each of the one or more PRACHinstances of the second set use the same Zadoff-Chu sequence.
 26. Theapparatus of claim 25, wherein the one or more processing elements arefurther configured to: prior to said transmitting the first set of oneor more PRACH instances, receive system information from a base station,wherein the system information indicates at least the conventionalformat.
 27. The apparatus of claim 25, wherein a PRACH configuration foreach subframe of the first set and for each subframe of the second setis identical.